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Article

The Attractiveness of the Ternary Rh-Pd-Pt Alloys for CO Oxidation Process

by
Aleksey A. Vedyagin
1,*,
Yury V. Shubin
2,
Roman M. Kenzhin
1,
Pavel E. Plyusnin
2 and
Vladimir O. Stoyanovskii
1
1
Boreskov Institute of Catalysis SB RAS, Department of Materials Science and Functional Materials, 630090 Novosibirsk, Russia
2
Nikolaev Institute of Inorganic Chemistry SB RAS, Department of Chemistry of Coordination, Cluster and Supramolecular Compounds, 630090 Novosibirsk, Russia
*
Author to whom correspondence should be addressed.
Processes 2020, 8(8), 928; https://doi.org/10.3390/pr8080928
Submission received: 8 July 2020 / Revised: 29 July 2020 / Accepted: 30 July 2020 / Published: 2 August 2020
(This article belongs to the Special Issue Recent Advances in Catalysis by Transition Metals)
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Abstract

:
Ternary alloys of platinum group metals attract a growing interest due to their unique catalytic properties. The present research is aimed to synthesize a series of Rh-Pd-Pt alloys with varied ratios of metals using a single-source precursor approach. Rhodium and palladium are partly miscible metals, while each of these metals is unlimitedly miscible with platinum. Thermolysis of complex salts used as a precursor results in the formation of metastable systems. The 3D nanostructure alloys are being formed after the complete decomposition of the single-source precursor. High-resolution transmission electron microscopic studies have shown that the nanoalloys are composed of interconnected polycrystalline ligaments with a mean diameter of 50 nm. The single-phase composition is confirmed by an X-ray diffraction analysis. The ratio of metals plays an important role in determining the catalytic activity of alumina-supported alloys and their thermal stability. According to UV-vis spectroscopy data, the higher palladium portion corresponds to worse dispersion of initially prepared, fresh catalysts. Treatment of the catalysts under prompt thermal aging conditions (up to 800 °C) causes redispersion of palladium-rich alloyed nanoparticles, thus leading to improved catalytic activity and thermal stability.

1. Introduction

Currently, a growing interest is attracted by metallic nanoparticles consisting of two and more metals with a specified interaction between them. Such nano-objects exhibit unique properties in various fields of application [1,2,3,4,5,6,7]. Thereby, one of the actual challenges of modern materials science is the development of the preparation routes to obtain metallic nanoparticles with a predefined size, composition, and, finally, properties. Among the variety of metals efficiently used in catalytic processes, precious metals of platinum group (Pt, Pd, and Rh) are of special importance. The palladium-based catalysts are known as highly active and efficient in a wide range of heterogeneous reactions starting from fine organic synthesis to partial and complete oxidation, selective hydrogenation or dehydrogenation [8,9,10,11,12,13,14,15,16,17,18,19,20,21]. For instance, being deposited on oxide supports (ceria, zirconia, alumina, etc.), Pd provides complete oxidation of hydrocarbons and CO that makes it a significant component of the modern catalysts of the engine exhaust gases purification [22,23,24,25,26,27,28,29]. Platinum is widely applied in numerous industrially important catalytic processes including hydrogenation (hydrogenation of C=C, C=O, N=O, and C≡N bonds), dehydrogenation (cleavage of N-H and C-H bonds), reforming of oxygenates (alcohols, polyols, and other), CO oxidation, water gas shift reaction, conversion of CH4, hydrodechlorination, as well as in fuel cells [30,31,32,33,34,35,36,37,38]. Rhodium is famous due to its ability to activate and reduce nitrogen oxides. This feature made it to be another essential component of the onboard emission control systems [39]. Along with this, Rh can catalyze the most of the reactions traditionally performed over Pd and Pt catalysts [40,41,42,43,44,45,46,47,48].
All these metals were recently reported to show a synergetic effect in terms of activity and/or stability being alloyed with other metals. Most often, bimetallic systems are used for this purpose. Thus, the oxidative function of palladium can be noticeably enhanced by modifying with Ni, Fe, Cr, Cu, Co, Ag, etc. [49,50,51,52,53,54,55]. Platinum catalysts were doped with Ni, Au, and Cu [6,30,56,57]. Alloying of palladium and platinum with rhodium was numerously reported to improve the thermal stability of the catalysts and widen their functionality [58,59,60,61,62,63,64,65,66,67,68]. It is important to note that Pd and Rh are partly miscible metals [69]. Their miscibility diagram is represented by a large gap, and the thermodynamically stable alloys cannot exist within this immiscibility area. As it was shown recently, the Pd/Rh ratio in the alloy plays an important role in catalytic behavior of the alumina-supported catalysts [70]. The highest resistance towards high-temperature aging was exhibited by the system with the Pd/Rh ratio of 3/2. Moreover, this ratio affects the mechanism of the oxidation/reduction reactions taking place. A decrease in the rhodium portion diminishes the involvement of NO species into oxidation of hydrocarbons. The best performance corresponds to the mentioned area of immiscibility when the Pd-Rh alloy is metastable. To prepare securely the metastable alloys, a single precursor concept is shown to be the most efficient [68,71]. Platinum is miscible with both metals without any limits, and there are no problems to synthesize bimetallic Pt-Pd or Pt-Rh alloys with any desired ratio.
During the last decades, ternary alloyed systems, containing Pd, Pt, and Rh, attract more and more attention of the research [43,72,73,74,75,76,77,78,79,80,81]. The synergistically improved efficiency was proved for the selective catalytic oxidation of ammonia, oxidation of hydrocarbons, including substituted ones, and oxidation of CO. Thereby, ternary Pt-Pd-Rh alloys are the perspective to be used in three-way catalysts. It should be noted that each of these metals being supported on oxide carriers is characterized by specific behavior at elevated temperatures. Palladium species undergo surface migration and agglomeration into relatively large particles [82]. Rhodium ions can diffuse into the bulk of the alumina support, where they initiate local phase transformations leading to the formation of the corundum phase [83]. Both these processes are responsible for the deactivation of catalysts. At the same time, agglomeration of palladium can be considered as a reversible process, since at temperatures of 800 °C formed Pd (PdO) particles can undergo redispersion, [84,85,86,87,88] while for rhodium ions the deactivation is irreversible due to their encapsulation inside the α-Al2O3 phase. Alloying of Pd with Rh helps to prevent both these deactivation processes. Platinum is the most tolerant metal towards high-temperature aging among the considered trio [89]. In the case when all the metals are alloyed together, high-temperature treatment faces another problem of their segregation. Liu et al. have reported that platinum and palladium atoms prefer to segregate on the surface of the alloyed nanoparticle, while rhodium atoms tend to aggregate inside [80]. Palladium atoms are characterized by stronger surface segregation if compare with platinum ones. Enrichment of the surface of bimetallic Pd-Rh and trimetallic Pt-Pd-Rh alloys was theoretically justified by Chen et al. using the modified analytical embedded atom method combined with Monte Carlo computer simulations [74]. In the case of ternary alloy, the surface Pd concentration is influenced by bulk Rh compositions.
Taking into account all the trends existing in the literature, the present research aims to synthesize the ternary Rh2(PdxPt1-x)3 alloys with varied Pd/Pt ratio using a single precursor approach and study the physicochemical properties, catalytic activity in CO oxidation and thermal stability at elevated temperatures. The phase composition of the prepared samples is examined using an X-ray diffraction analysis. Catalytic activity and thermal stability are studied in a prompt thermal aging regime [90]. The state of palladium in fresh and aged catalysts is estimated using UV-vis spectroscopy.

2. Materials and Methods

2.1. Synthesis of Precursors

In the present work, single-source precursors [RhEn3]2[Pd(NO2)4]3, [RhEn3]2[Pt(NO2)4]3, and [RhEn3]2[PdxPt1−x(NO2)4]3, where En is ethylenediamine C2H8N2, were synthesized according to the following procedures.
[RhEn3]2[Pd(NO2)4]3: 4 mL of K2[Pd(NO2)4] aqueous solution (623 mg, 1.5 mmol) was added to 3 mL of [RhEn3]Cl3·3H2O aqueous solution (500 mg, 1 mmol) at continuous stirring. The sediment was filtered using a porous glass filter, washed with 3 mL of ice water and 5 mL of ethanol. The yield of the double complex salt was 63% (450 mg).
[RhEn3]2[Pt(NO2)4]3: 8 mL of K2[Pt(NO2)4] aqueous solution (533.2 mg, 1.1 mmol) was added to 2 mL of [RhEn3]Cl3·3H2O aqueous solution (312.4 mg, 0.7 mmol) at continuous stirring. The sediment was filtered and washed as described above. The yield of the double complex salt was 67% (200 mg).
The double complex salts containing three metals were obtained by mixing of [RhEn3]Cl3·3H2O aqueous solution with a joint solution of K2[Pt(NO2)4] and K2[Pd(NO2)4] taken in an appropriate ratio. For instance, [RhEn3]2[Pd0.5Pt0.5(NO2)4]3 was prepared by mixing 3 mL of K2[Pt(NO2)4] aqueous solution (145.87 mg, 0.29 mmol) and 3 mL of K2[Pd(NO2)4] aqueous solution (117.6 mg, 0.29 mmol) with 1 mL of [RhEn3]Cl3·3H2O aqueous solution (169.5 mg, 0.38 mmol) at continuous stirring. The sediment was filtered and washed as described above. The yield of the double complex salt was 44% (130 mg).

2.2. Synthesis of Catalysts

The samples for the catalytic testing were prepared by an incipient wetness impregnation of commercial alumina powder (Puralox TH 100/150; Sasol, Germany) with aqueous solutions of the double complex salts at room temperature under continuous stirring. Then, the samples undergo drying at 105 °C for 12 h and calcination at 400 °C for 1 h. The total metal loading of Pt, Pd, and Rh was 0.2 wt %. The ratio of (Pd+Pt)/Rh was 3/2, while the Pd/Pt ratio was varied as 3/1, 1/1, and 1/3. The resulting samples were marked as Rh2(Pd0.75Pt0.25)3/γ-Al2O3, Rh2(Pd0.5Pt0.5)3/γ-Al2O3, and Rh2(Pd0.25Pt0.75)3/γ-Al2O3. The reference samples Pd/γ-Al2O3, Pt/γ-Al2O3, Rh2Pd3/γ-Al2O3, and Rh2Pt3/γ-Al2O3 were obtained by similar procedures.

2.3. Characterization Techniques

The powder X-ray diffraction (XRD) analysis of the prepared precursors and alloys was performed at room temperature and atmospheric pressure on a Shimadzu XRD-7000 diffractometer (Shimadzu Corp., Kyoto, Japan) operating with CuKα radiation, nickel filter in reflected beam, and scintillation detector with amplitude discrimination. The data were collected step-by-step in the range of angles 2θ = 5–135° with a step of 0.05°. The resulting patterns were analyzed and fitted using a PowerCell 2.4 and WINFIT 1.2.1 software packages, correspondingly [91,92]. The obtained coordination compounds were single-phase, which was identified by indexing the powder XRD patterns similarly to theoretical patterns for complexes studied by an X-ray structure analysis.
Elemental (C, H, and N) analysis was carried out on a Euro EA 3000 analyzer (Eurovector, S.p.a., Milan, Italy). The specimen was thermally destroyed in the presence of solid oxidizers with the addition of gaseous oxygen until the quantitative formation of final products: CO2, water, and nitrogen. The obtained gas mixture was separated chromatographically. The quantities of the components were used to calculate the portions (wt %) of carbon, hydrogen, and nitrogen in the analyzed sample.
The metal content in the samples was determined by the atomic absorption method using a Hitachi Z-800 spectrometer (Hitachi, Tokyo, Japan). The sample was dissolved in aqua regia, evaporated until the minimal volume, loaded into a graduated flask and diluted by distilled water until marker.
All the theoretical values of the element’s content were calculated from the molecular weights of the coordination compounds.
The metal loading in the supported catalysts was measured by an energy dispersive X-ray fluorescence (ED XRF) analysis. An M1 MISTRAL spectrometer (Bruker Nano Nano GmbH, Berlin, Germany) with a microfocus X-ray tube (W-anode) and a high-resolution silicon drift detector (SDD, energy resolution <150 eV at Mn-Kα) was used.
Thermogravimetric analyses (TGA) were carried out using a TG 209 F1 Iris thermobalance (NETZSCH-Gerätebau GmbH, Selb, Germany). Synchronic thermal analysis was performed using an STA 449F1 Jupiter analyzer equipped with a QMS 403D Aëolos quadrupole mass spectrometer (NETZSCH-Gerätebau GmbH, Selb, Germany). The measurements were made in a hydrogen–helium mixture (10% vol. H2 in He). The parameters of the TGA experiments were the following: sample weight of 20 mg; Al-crucibles; the gas flow rate of 60 mL/min; and the temperature ramping rate of 10 °C/min.
The high-resolution transmission electron microscopy (HR TEM) measurements were performed using a JEM-2010 electron microscope (JEOL Ltd., Tokyo, Japan) with lattice plane resolution 0.14 nm at an accelerating voltage of 200 kV. Images of periodic structures were analyzed by the Fourier method. A local energy-dispersive X-ray analysis (EDXA) was carried out using an EDX spectrometer Xflash (Bruker Nano GmbH, Berlin, Germany) fitted with a Si detector with a resolution of 128 eV. The samples for the HR TEM study were prepared on a perforated carbon film mounted on a copper grid.
Diffuse reflectance UV-Vis spectra were recorded between 200 and 850 nm using a UV-vis spectrometer UV-VIS 2501 PC (Shimadzu Corp., Kyoto, Japan) with IRS-250A diffusion reflection attachment. The UV-vis spectra were transformed into the Kubelka–Munk function F(R) calculated as F(R) = (1 − R)2/2R, where R is the experimentally measured reflectivity coefficient of the samples [93].

2.4. Testing the Catalytic Activity in the Oxidation of CO

The catalytic performance of the alumina-supported catalysts was examined in a model reaction of CO oxidation. Each sample was studied in seven consecutive cycles under prompt thermal aging (PTA) conditions as described elsewhere [90,93,94,95,96]. The testing procedure was as follows. The sample (300 mg) was loaded into the quartz flow reactor, and then the reaction mixture contained 0.15 vol% CO, 14.0 vol% O2, 0.01 vol% NO, 0.01 vol% hydrocarbons (a mixture of methane, propylene, and toluene), and nitrogen (as balance) was passed through the reactor. The flow rate was 334 mL/min. A temperature ramping rate was 10 °C/min. The final temperature of the catalytic cycle was 320 °C for 1st and 2nd cycles, 600 °C for 3rd and 4th cycles, and 800 °C for the last three cycles. The CO concentration at the reactor outlet was registered by a gas analyzer ULTRAMAT 6 (Siemens). The temperature of 50% CO conversion (T50) was used as a criterion to compare the thermal stability of the catalysts.

3. Results and Discussion

3.1. Characterization of the Precursors

At the first step of the study, all the prepared coordination compounds were characterized by elemental analysis, atomic absorption spectroscopy, and infrared spectroscopy. The elemental compositions of [RhEn3]2[Pd(NO2)4]3, [RhEn3]2[Pt(NO2)4]3, and [RhEn3]2[Pd0.5Pt0.5(NO2)4]3 salts are presented in Table 1. The infrared spectra of the prepared coordination compounds are shown in Figure 1a and the corresponding oscillation frequencies are summarized in Table 2. As seen, the measured values of elements content were very close to the calculated ones. The results of the infrared spectroscopy (Table 2) allowed identifying of the functional groups in the compositions of the salts.
The obtained double complex salts [RhEn3]2[Pd(NO2)4]3 and [RhEn3]2[Pt(NO2)4]3 and their solid solutions with varied ratios of metals in the anionic part were easily isolated into the solid phase in the nonaqueous form. Both the purity and the single phase of all the synthesized products were confirmed by an XRD analysis method (Figure 1b). As follows from the figure, the experimental patterns corresponded well with the simulated (calculated) one.
The thermal decomposition of [RhEn3]2[Pd(NO2)4]3 salt in a hydrogen medium was recently reported in detail [96]. The thermolysis of the double complex salt [RhEn3]2[Pd(NO2)4]3 and the solid solutions of [RhEn3]2[PdxPt1−x(NO2)4]3 composition in a reductive medium proceeded similarly, in few hardly separable stages accompanied by exothermic effects (Figure 2a). Along with this, the thermal stability of the solid solutions depends on the content of palladium in their composition (Figure 2b). The starting temperature point of decomposition regularly decreased with an increase of the palladium content due to the lower thermal stability of the Pd-containing coordination compounds. The final temperature point of decomposition was not changed noticeably and corresponded to 310–320 °C. The total weight loss and the weight of the products obtained by pyrolysis in a reductive atmosphere agreed well with the calculated content of metals in the composition of the initial single-source precursors (Table 3).

3.2. Characterization of the Alloys

Some representative TEM images of the products of the precursors’ thermolysis are shown in Figure 3. The decomposition of the precursors in a hydrogen atmosphere along with subsequent heating of the products up to 600 °C resulted in the formation of an alloy characterized by a porous sponge-like structure. In terms of morphology, the nanoporous alloys consisted of interconnecting ligaments with a mean diameter of 50 nm. As evidenced by HR TEM, the ligaments were polycrystalline with grain boundaries separated by a few nanometers.
An energy-dispersive spectroscopic study of the as-prepared samples confirmed that the Rh:Pd:Pt atomic ratio in alloys was consistent with the atomic ratio of metals in the respective precursors. The alloy nature of the porous products was also confirmed by estimation of the interplanar spacing (d111) from the high-resolution TEM images (Figure 3). The estimated mean values of the interplanar spacing correlated satisfactorily with the corresponding d111 values calculated from the lattice parameters obtained by the XRD analysis method (Table 4).
It should be noted that the binary systems Pt-Pd, Rh-Pt, and Rh-Pd were characterized by a wide area of existence of the random solid solutions with face-centered cubic cell (fcc, space group Fm3m) [69,97,98,99,100,101]. In all these binary systems the components were miscible at the temperatures above 900 °C in a whole range of compositions. The Rh-Pd system exhibited a miscibility gap with the critical point of solubility at 58 at.% Rh and 820 °C [69].
Up to date, there is no information concerning an experimental study on the subsolidus area of the ternary Rh-Pd-Pt system. The only exception is the reported isothermal section at 1200 °C illustrating the unlimited miscibility of the components at this temperature in a whole range of compositions [102,103]. Therefore, the hypothetical scheme of the phase diagram for this ternary system can be based on the extrapolations from the binary Pt-Pd, Rh-Pt, and Rh-Pd systems only. Additionally, it should be taken into account that since the binary Rh-Pd alloy separated onto two phases at temperatures below 820 °C, the phase diagram of the ternary system was characterized by a presence of the miscibility gap, which should be based on the Rh-Pd axis. The first attempt to draw the phase diagram for the Rh-Pd-Pt system was undertaken using the calculations of the heats of mixing by the Monte Carlo (MC) method combined with the semi-empirical modified embedded atom method (MEAM). The resulting miscibility gap for the temperature of 327 °C is presented in Figure 4. Taking into account the experimental temperature dependency of the equilibrium solubility of the solid solutions in the Rh–Pd system and the isothermal cross-section of the ternary phase diagram for the Rh-Pd-Pt system at 327 °C, the hypothetical miscibility gaps for the temperatures 600, 700, and 800 °C are drawn in Figure 4. As seen from the presumed ternary phase diagrams, the alloys Rh2(Pd0.25Pt0.75)3, Rh2(Pd0.5Pt0.5)3, and Rh2Pt3 at 600 °C and above (filled triangles) were located in a homogeneous area and, therefore, should be in equilibrium. Contrary, the Rh2Pd3 and Rh2(Pd0.75Pt0.25)3 alloys at the same temperatures (empty triangles) should be metastable.
Processes 08 00928 g004 550
Figure 4. The phase diagram of the Rh-Pd-Pt alloy. The calculated miscibility gap is based on data reported by Luyten et al. [104]. The colored squares correspond to experimental points for the binary Pd-Rh systems at temperatures of 600, 700, and 800 °C, while dash lines show the estimated miscibility gaps for the ternary Rh-Pd-Pt systems at these temperatures. Red triangles are experimental points for the alloys studied in the present work, where filled and empty triangles lie in areas of homogeneity and metastability, accordingly.
Figure 4. The phase diagram of the Rh-Pd-Pt alloy. The calculated miscibility gap is based on data reported by Luyten et al. [104]. The colored squares correspond to experimental points for the binary Pd-Rh systems at temperatures of 600, 700, and 800 °C, while dash lines show the estimated miscibility gaps for the ternary Rh-Pd-Pt systems at these temperatures. Red triangles are experimental points for the alloys studied in the present work, where filled and empty triangles lie in areas of homogeneity and metastability, accordingly.
Processes 08 00928 g004
Table
Table 4. The ratio of metals and the crystal lattice parameters in the prepared nanoalloys.
Table 4. The ratio of metals and the crystal lattice parameters in the prepared nanoalloys.
SampleLattice Parameter, a, Åd111 (calc.) **, Åd111 (TEM), ÅRh:Pd:Pt (EDX)
Rh3.803 *2.196--
Pd3.890 *2.246--
Pt3.923 *2.265--
Rh2Pd33.8562.2262.2238:62:0
Rh2(Pd0.75Pt0.25)33.8612.2292.2337:53:10
Rh2(Pd0.50Pt0.50)33.8652.2312.2339:40:21
Rh2(Pd0.25Pt0.75)33.872.2342.2438:22:40
Rh2Pt33.8772.2382.2443:00:57
* The lattice parameters are taken from the ICDD PDF-2 database [105]; ** The values are calculated from the lattice parameter.
The XRD patterns of the products obtained by the decomposition of the single-source precursors [RhEn3]2[Pd(NO2)4]3, [RhEn3]2[Pt(NO2)4]3, [RhEn3]2[Pd0.75Pt0.25(NO2)4]3, [RhEn3]2[Pd0.5Pt0.5(NO2)4]3, and [RhEn3]2[Pd0.25Pt0.75(NO2)4]3 at 600 °C in a hydrogen atmosphere are presented in Figure 5. As seen, they contained only the fcc phase (Figure 5a). The shift in the position of the reflexes regarding pure Pd, Pt, and Rh was observed in a far angle region (Figure 5b). This indicates the formation of homogeneous solid solutions. The analysis of the reflexes position allowed the conclusion that an increase of the Pd content in the ternary alloy composition leads to the shifting of the reflexes towards a far angle region, thus testifying in a decrease in the parameter of the elementary cell of the solid solution. The lattice parameters of the alloys calculated from the positions of 331 and 420 reflexes are summarized in Table 4.
Figure 6 shows the dependencies of the lattice parameters of the alloys on the atomic fraction in the Rh-Pt and Rh-Pd systems based on the literature data [69,101,106]. In these binary systems, an appropriate satisfiability of the Vegard’s law was observed. The maximum deviation of the lattice parameters from the law did not exceed 0.002 Å. Taking all these into account, interpolating isotherms ’lattice parameter—composition’ for the ternary Rh-Pd-Pt alloys are plotted in Figure 6 (dashed lines).
The measured values of lattice parameters of the ternary alloys (Figure 6, triangles) matched the corresponding values on the plotted dependencies. Thereby, this confirms a coincidence of the composition of the synthesized homogeneous ternary solid solutions with the composition specified at the synthesis of the single-source precursors.

3.3. Characterization and Testing of the Alumina-Supported Catalysts

In the next step of the study, the synthesized precursors were supported on the commercial alumina powder via an incipient wetness impregnation. In order to control the content of the supported metals, the catalysts samples were characterized by an ED XRF method. The measured values along with the calculated ones are summarized in Table 5. As seen, the values coincided with a good enough accuracy.
All the samples of alumina-supported catalysts were tested in a model reaction of CO oxidation. The testing procedure was performed under prompt thermal aging conditions, which allowed monitoring of the degradation of the catalysts during the high-temperature exposure. The corresponding light-off curves are shown in Figure 7a–e. To compare the samples evidently, the dependencies of the T50 parameter on the catalytic run number are plotted in Figure 7f. The platinum-only catalyst was used as a reference sample. As follows from the obtained results, the metals in the alloy interacted with each other and influence the catalytic properties of the catalyst as a whole. For instance, Pt/γ-Al2O3 sample demonstrated poor initial activity (T50 = 286 °C) but undergoes reactivation at elevated temperatures. Most significantly this effect became apparent after heating up to 800 °C. In the case of the bimetallic Rh2Pt3/γ-Al2O3 catalyst, the tendencies in catalytic activity and stability remained the same. In general, the presence of rhodium in the catalyst’s composition made the catalyst a little bit more active. For the ternary alloy systems, a partial replacement of platinum with palladium much evidently enhanced the initial activity of the catalyst: more Pd content in the alloy corresponded to the lower value of the T50 parameter. Since palladium is known to be less stable than platinum, the aging of the catalysts at 600 °C led to their noticeable deactivation. Then, being heated up to 800 °C, Rh2(Pd0.25Pt0.75)3/γ-Al2O3 and Rh2(Pd0.5Pt0.5)3/γ-Al2O3 catalysts show reactivation similarly to the samples without palladium. Oppositely, the sample Rh2(Pd0.75Pt0.25)3/γ-Al2O3 containing a higher amount of Pd continued to deactivate even after treatment at 800 °C. Taking into account the mentioned oppositely directed trends, it could be concluded the most promising system is a ternary alloy Rh2(Pd0.5Pt0.5)3 with an equivalent amount of palladium and platinum. At a higher content of Pd, the “metal–metal” interactions in the alloy were assumed to become weaker due to partial immiscibility of palladium and rhodium, and the further catalytic behavior of the catalyst was determined by Pd. If platinum dominates over palladium, then the catalyst performs worse activity.
As we have reported recently, optical spectroscopy methods are useful and informative tools allowing characterizing of the state of the supported precious metals and their alloys as well as the changes taking place during high-temperature aging [93]. Therefore, all the studied binary and ternary catalysts and the monometallic reference samples were examined by a diffuse reflectance UV-vis spectroscopy. To exclude the effect of “metal–metal” interactions, some additional reference samples obtained by mechanical mixing of corresponding monometallic catalysts were prepared and studied.
Figure 8 presents the UV-vis spectra for the monometallic Pt/γ-Al2O3 and Rh/γ-Al2O3, samples and the bimetallic Rh2Pt3/γ-Al2O3 (alloy) and Rh+Pt/γ-Al2O3 (mechanical mixture) catalysts. To study the effect of the surface hydroxylation under natural conditions, the Pt/γ-Al2O3 sample was additionally calcined in argon at 400 °C for 4 h immediately before the measurements. Such a low temperature of pretreatment was chosen to minimize any possible sintering effects. As known, the spectra of the Rh3+ (4d6) and Pt4+ (5d6) ions in the low-spin octahedral complexes are characterized by a charge transfer band and d-d transitions 1A1g → 1T1g, 1T2g. The representative value of the energy-gap width (Eg) of Rh3+ complexes for the Rh/γ-Al2O3 sample was equal to 2.49 eV (Figure 8, spectrum 2). Koffyberg has reported that the Eg value for Rh2O3 particles decreases from an asymptotic value of 2.59 eV for the isolated Rh3+ complexes to 1.2 eV for the bulk oxide Rh2O3 [107].
In the case of the Pt/γ-Al2O3 sample, the energy-gap width for Pt4+ complexes was about 2.62 eV. This value did not change noticeably after the dehydroxylation procedure in an argon flow at 400 °C, despite a slight increase in the intensity of the 1A1g → 1T1g band. Unfortunately, there is no information on the Eg value for the Pt4+ complexes in the literature. The experimental Eg values for the α-PtO2 particles were varied in a range from 1.3 [108],to 1.8 eV [109].
As evident from Figure 8, the sum of spectra 1 and 2 (Pt/γ-Al2O3 and Rh/γ-Al2O3 samples, accordingly) corresponded well to the spectra for the bimetallic samples Rh2Pt3/γ-Al2O3 and Rh+Pt/γ-Al2O3, despite the lower intensity. Such an approach was recently reported as efficient for the approximation of spectra of the bimetallic Rh2Pd3/γ-Al2O3 model catalysts [95]. Good agreement of the spectra for the binary systems with the spectra for the monometallic reference samples indicates that there were no significant distortions of the octahedral surrounding taking place during the formation of Rh2Pd3 oxide clusters. Long-wave edge of d-d transitions of the bimetallic samples at the present ratio of metals was mainly determined by Rh3+ ions. The values of the energy-gap width for the samples Rh2Pt3/γ-Al2O3 and Rh+Pt/γ-Al2O3 were equal to 2.47 and 2.34 eV, respectively. The sample Rh+Pt/γ-Al2O3 was characterized by a larger particle size in comparison with the sample Rh2Pt3/γ-Al2O3, which possessed practically the same Eg value as the reference sample Rh/γ-Al2O3.
Figure 9a shows the UV-vis spectra for the samples of the reference catalyst Pt/γ-Al2O3 treated at 400 °C (spectrum 2), aged under PTA conditions (spectrum 1), and treated in air at 400 °C for 6 h after aging under PTA conditions (spectrum 3). Left part of these spectra presented in Figure 9b demonstrates the charge transfer band for the same samples. Treatment in air was aimed to oxidize the reduced part of platinum and recover the initial hydroxyl coverage on the surface without any sintering effects. The observed appearance of an intensive band of the plasmon resonance in the UV region of the spectrum 1 testifies towards the formation of Pt0 particles, while d-d transitions indicate the presence of oxidized Pt4+ species. The shift of the 1A1g → 1T2g band to the short-wave region can be assigned to the part exchange of the ligands in the Pt4+ complexes as a result of aging in the PTA regime, and to their interaction with metallic particles. The oxidative treatment of the catalyst in air leads to a decrease in intensity of the band in the UV region of the spectrum down to the initial level, thus indicating the oxidation of platinum. On the other hand, an increase in the intensity of d-d transitions of the Pt4+ complexes along with a shift of the absorption band’s edge towards the long-wave region allows the conclusion about the formation of relatively large α–PtO2 particles characterized by the Eg value of 1.65 eV.
The UV-vis spectra for the bimetallic catalysts Rh2Pt3/γ-Al2O3 and Rh+Pt/γ-Al2O3 and monometallic reference sample Pt/γ-Al2O3 after the prompt thermal aging experiments and subsequent treatment in air at 400 °C are shown in Figure 10. Corresponding values of the energy-gap width for the initial and aged samples are summarized in Table 6. It was evident that both the bimetallic samples were more thermally stable towards sintering if compared with the Pt/γ-Al2O3 reference, and possessed very close values of Eg 1.97–2.01 eV.
The UV-vis spectra for the ternary systems Rh2(Pd0.25Pt0.75)3/γ-Al2O3, Rh2(Pd0.5Pt0.5)3/γ-Al2O3, and Rh2(Pd0.75Pt0.25)3/γ-Al2O3 before and after the aging under PTA conditions are shown in Figure 11. In the initial state, the values of the energy-gap width for these catalysts were very close (Table 6). The sample Rh2(Pd0.25Pt0.75)3/γ-Al2O3 containing the highest amount of platinum was characterized by a better dispersion of the alloy nanoparticles (Figure 11a). The aging of the samples at 800 °C changed significantly the situation. In this case, the samples could be ranked by a decreased dispersion as Rh2(Pd0.75Pt0.25)3/γ-Al2O3 > Rh2(Pd0.5Pt0.5)3/γ-Al2O3 > Rh2(Pd0.25Pt0.75)3/γ-Al2O3. The Eg values for the samples Rh2(Pd0.75Pt0.25)3/γ-Al2O3 and Rh2(Pd0.5Pt0.5)3/γ-Al2O3 were 2.3 and 2.17 eV, accordingly. Thereby, in terms of dispersion of the active component, the ternary alloy systems surpassed the bimetallic and monometallic catalysts.
It was already mentioned that the Pt-only catalyst underwent noticeable reactivation after the aging at 800 °C. Its catalytic activity in the 6th and 7th runs was comparable with that for the binary and ternary catalysts (Figure 7). On the other hand, as it follows from the UV-vis spectroscopy data (Figure 9a), the active Pt species after the PTA aging were predominantly represented by the Pt4+ complexes. For the ternary systems, the higher amount of these forms is observed in the case of Rh2(Pd0.5Pt0.5)3/γ-Al2O3 (Figure 11, spectrum 2). Possibly, this explains the better catalytic performance (high initial activity and appropriate stability) of this sample.
Summarizing all the data presented above, it should be mentioned that the concept of a single-source precursor is applicable and quite efficient for the preparation of the supported ternary Rh-Pd-Pt catalysts. The thermolysis of the solid solutions of the double complex salts used as such precursors allows for obtaining of the ternary alloys with a predefined metal ratio. Thus, the final catalytic properties of the catalysts can be easily tuned.

4. Conclusions

Precious metals supported on different supports (alumina, ceria, and zirconia) are widely attractive due to their excellent catalytic properties in various industrially and environmentally important processes. For instance, one of the areas of their application is three-way catalysis aimed to reduce the emissions from gasoline engines. The requirements imposed for such catalytic converters are an appropriate activity in the catalyzed reactions (oxidation of CO and hydrocarbons, and reduction of nitrogen oxides) and long-term stability including the resistance towards the elevated temperatures. The CO oxidation reaction is commonly used as a model reaction for screening the prospective catalytic compositions. The present work is purposed in studying the applicability of a single-source precursor concept to prepare the ternary nanoalloys with improved catalytic characteristics. A series of the catalysts were prepared by an incipient wetness impregnation of the alumina support with an aqueous solution of the corresponding complex salt containing one, two, or three metals (Rh, Pd, and Pt). The formation of alloys as a result of the precursor’s thermolysis in a reductive medium was confirmed by the XRD and TEM methods. The phase diagram for the ternary Rh-Pd-Pt system at temperatures 600, 700, and 800 °C was proposed for the first time. The prepared samples were examined in the CO oxidation reaction performed under prompt thermal aging conditions. It was shown that the introduction of palladium into the composition of the active particles improves the initial activity along with appropriate stability at high temperatures. The best catalytic performance was exhibited by the Rh2(Pd0.5Pt0.5)3/γ-Al2O3 sample with equal amounts of platinum and palladium. The characterization of the catalysts by a diffuse reflectance UV-vis spectroscopy has revealed that palladium affects the dispersion of the nanoparticles: the higher the amount of Pd that is introduced, the better dispersion is. The extraordinary activity of the Rh2(Pd0.5Pt0.5)3/γ-Al2O3 sample is assigned to the presence of Pt in the form of the Pt4+ complexes.

Author Contributions

Conceptualization, A.A.V. and Y.V.S.; methodology, A.A.V. and Y.V.S.; investigation, R.M.K., P.E.P. and V.O.S.; writing—original draft preparation, A.A.V., Y.V.S. and P.E.P.; writing—review and editing, A.A.V.; project administration, Y.V.S.; funding acquisition, Y.V.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Russian Science Foundation, grant number 16-13-10192.

Acknowledgments

Characterization of the samples was performed using the equipment of the Center of Collective Use “National Center of Catalysts Research”.

Conflicts of Interest

The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

References

  1. Cheng, D.; Xu, H.; Fortunelli, A. Tuning the catalytic activity of Au–Pd nanoalloys in CO oxidation via composition. J. Catal. 2014, 314, 47–55. [Google Scholar] [CrossRef]
  2. Kang, N.; Ng, M.S.; Shan, S.; Wu, J.; Zhao, W.; Yin, J.; Fang, W.; Luo, J.; Petkov, V.; Zhong, C.-J. Synergistic catalytic properties of bifunctional nanoalloy catalysts in rechargeable lithium-oxygen battery. J. Power Sources 2016, 326, 60–69. [Google Scholar] [CrossRef] [Green Version]
  3. Ruiz-Ruiz, V.-F.; González-Olvera, R.; Díaz-Pardo, R.; Betancourt, I.; Zumeta-Dubé, I.; Díaz, D.; Farfán, N.; Arellano-Jiménez, M.J. Mechanochemically obtained Pd–Ag nanoalloys. Structural considerations and catalytic activity. Materialia 2018, 4, 166–174. [Google Scholar] [CrossRef]
  4. Zhang, Y.; Gao, F.; Fu, M.-L. Composite of Au-Pd nanoalloys/reduced graphene oxide toward catalytic selective organic transformation to fine chemicals. Chem. Phys. Lett. 2018, 691, 61–67. [Google Scholar] [CrossRef]
  5. Taran, S. Composition effect on melting behaviors of Cu-Au-Pt trimetallic nanoalloys. Comput. Theor. Chem. 2019, 1166, 112576. [Google Scholar] [CrossRef]
  6. Campos-Roldán, C.A.; Calvillo, L.; Granozzi, G.; Alonso-Vante, N. Alkaline hydrogen electrode and oxygen reduction reaction on PtxNi nanoalloys. J. Electroanal. Chem. 2020, 857, 113449. [Google Scholar] [CrossRef]
  7. Liu, X.; Wu, J.; Guo, X. Ternary boron-, phosphorus- and oxygen-doped amorphous nickel nanoalloys for enhanced activity towards the oxygen evolution reaction. Electrochem. Commun. 2020, 111, 106649. [Google Scholar] [CrossRef]
  8. Cizmeci, M.; Musavi, A.; Tekin, A.; Kayahan, M. Comparison of two palladium catalysts on different supports during hydrogenation. J. Am. Oil Chem. Soc. 2006, 83, 1063–1068. [Google Scholar] [CrossRef]
  9. Vishwanathan, V.; Jayasri, V.; Mahaboob Basha, P. Vapor phase hydrogenation of o-chloronitrobenzene (o-CNB) over alumina supported palladium catalyst—A kinetic study. Reac. Kinet. Catal. Lett. 2007, 91, 291–298. [Google Scholar] [CrossRef]
  10. Fukuyama, T.; Kippo, T.; Ryu, I.; Sagae, T. Addition of allyl bromide to phenylacetylene catalyzed by palladium on alumina and its application to a continuous flow synthesis. Res. Chem. Intermediat. 2009, 35, 1053–1057. [Google Scholar] [CrossRef]
  11. Arora, S.; Kapoor, P.; Singla, M.L. Catalytic studies of palladium nanoparticles immobilized on alumina synthesized by a simple physical precipitation method. Reac. Kinet. Mech. Catal. 2010, 99, 157–165. [Google Scholar] [CrossRef]
  12. Hong, U.G.; Hwang, S.; Seo, J.G.; Yi, J.; Song, I.K. Hydrogenation of Succinic Acid to γ-Butyrolactone over Palladium Catalyst Supported on Mesoporous Alumina Xerogel. Catal. Lett. 2010, 138, 28–33. [Google Scholar] [CrossRef]
  13. Berenblyum, A.S.; Podoplelova, T.A.; Shamsiev, R.S.; Katsman, E.A.; Danyushevsky, V.Y. On the mechanism of catalytic conversion of fatty acids into hydrocarbons in the presence of palladium catalysts on alumina. Petroleum Chem. 2011, 51, 336–341. [Google Scholar] [CrossRef]
  14. Thomazeau, C.; Cseri, T.; Bisson, L.; Aguilhon, J.; Pham Minh, D.; Boissière, C.; Durupthy, O.; Sanchez, C. Nano Design of Alumina Supported Monometallic Catalysts: A Promising Way to Improve the Selective Hydrogenation of Poly-Unsaturated Hydrocarbons. Top. Catal. 2012, 55, 690–699. [Google Scholar] [CrossRef]
  15. Chen, L.; Feng, T.; Wang, P.; Xiang, Y.; Ou, B. Catalytic properties of Pd supported on hexaaluminate coated alumina in low temperature combustion of coal mine ventilation air methane. Kinet. Catal. 2013, 54, 767–772. [Google Scholar] [CrossRef]
  16. Voskanyan, P.S. Effect of the nature of a support on the catalytic activity of a palladium catalyst in the synthesis of vinyl acetate by gas-phase ethylene acetoxylation. Catal. Ind. 2013, 5, 90–97. [Google Scholar] [CrossRef]
  17. Weng, X.; Yuan, X.; Li, H.; Li, X.; Chen, M.; Wan, H. The study of the active surface for CO oxidation over supported Pd catalysts. Sci. China Chem. 2014, 58, 174–179. [Google Scholar] [CrossRef]
  18. Ravanchi, M.T.; Fadaeerayeni, S.; Fard, M.R. The effect of calcination temperature on physicochemical properties of alumina as a support for acetylene selective hydrogenation catalyst. Res. Chem. Intermediat. 2015, 42, 4797–4811. [Google Scholar] [CrossRef]
  19. Glyzdova, D.V.; Vedyagin, A.A.; Tsapina, A.M.; Kaichev, V.V.; Trigub, A.L.; Trenikhin, M.V.; Shlyapin, D.A.; Tsyrulnikov, P.G.; Lavrenov, A.V. A study on structural features of bimetallic Pd-M/C (M: Zn, Ga, Ag) catalysts for liquid-phase selective hydrogenation of acetylene. Appl. Catal. A-Gen. 2018, 563, 18–27. [Google Scholar] [CrossRef]
  20. Iost, K.N.; Borisov, V.A.; Temerev, V.L.; Surovikin, Y.V.; Pavluchenko, P.E.; Trenikhin, M.V.; Arbuzov, A.B.; Shlyapin, D.A.; Tsyrulnikov, P.G.; Vedyagin, A.A. Carbon support hydrogenation in Pd/C catalysts during reductive thermal treatment. Int. J. Hydrog. Energ. 2018, 43, 17656–17663. [Google Scholar] [CrossRef]
  21. Glyzdova, D.V.; Khramov, E.V.; Smirnova, N.S.; Prosvirin, I.P.; Bukhtiyarov, A.V.; Trenikhin, M.V.; Gulyaeva, T.I.; Vedyagin, A.A.; Shlyapin, D.A.; Lavrenov, A.V. Study on the active phase formation of Pd-Zn/Sibunit catalysts during the thermal treatment in hydrogen. Appl. Surf. Sci. 2019, 483, 730–741. [Google Scholar] [CrossRef]
  22. Monteiro, R.S.; Dieguez, L.C.; Schmal, M. The role of Pd precursors in the oxidation of carbon monoxide over Pd/Al2O3 and Pd/CeO2/Al2O3 catalysts. Catal. Today 2001, 65, 77–89. [Google Scholar] [CrossRef]
  23. Demoulin, O.; Navez, M.; Ruiz, P. The Activation of a Pd/γ-alumina Catalyst During Methane Combustion: Investigation of the Phenomenon and of Potential Causes. Catal. Lett. 2005, 103, 149–153. [Google Scholar] [CrossRef]
  24. Gopinath, R.; Babu, N.S.; Kumar, J.V.; Lingaiah, N.; Prasad, P.S. Influence of Pd Precursor and Method of Preparation on Hydrodechlorination Activity of Alumina Supported Palladium Catalysts. Catal. Lett. 2007, 120, 312–319. [Google Scholar] [CrossRef]
  25. Li, G.; Wang, Q.; Zhao, B.; Zhou, R. A new insight into the role of transition metals doping with CeO2–ZrO2 and its application in Pd-only three-way catalysts for automotive emission control. Fuel 2012, 92, 360–368. [Google Scholar] [CrossRef]
  26. Zhou, Y.; Wang, Z.; Liu, C. Perspective on CO oxidation over Pd-based catalysts. Catal. Sci. Technol. 2015, 5, 69–81. [Google Scholar] [CrossRef]
  27. Vedyagin, A.; Volodin, A.; Kenzhin, R.; Chesnokov, V.; Mishakov, I. CO Oxidation over Pd/ZrO2 Catalysts: Role of Support’s Donor Sites. Molecules 2016, 21, 1289. [Google Scholar] [CrossRef]
  28. Vedyagin, A.A.; Volodin, A.M.; Kenzhin, R.M.; Stoyanovskii, V.O.; Rogov, V.A.; Kriventsov, V.V.; Mishakov, I.V. The role of chemisorbed water in formation and stabilization of active sites on Pd/Alumina oxidation catalysts. Catal. Today 2018, 307, 102–110. [Google Scholar] [CrossRef]
  29. Ferri, D.; Elsener, M.; Kröcher, O. Methane oxidation over a honeycomb Pd-only three-way catalyst under static and periodic operation. Appl. Catal. B-Environ. 2018, 220, 67–77. [Google Scholar] [CrossRef]
  30. Yu, W.; Porosoff, M.D.; Chen, J.G. Review of Pt-Based Bimetallic Catalysis: From Model Surfaces to Supported Catalysts. Chem. Rev. 2012, 112, 5780–5817. [Google Scholar] [CrossRef]
  31. Kogan, S.B.; Herskowitz, M. Geometric and electronic factors in paraffin dehydrogenation on bimetallic platinum catalysts. Reac. Kinet. Catal. Lett. 2005, 85, 341–345. [Google Scholar] [CrossRef]
  32. Antolini, E. Formation, microstructural characteristics and stability of carbon supported platinum catalysts for low temperature fuel cells. J. Mater. Sci. 2003, 38, 2995–3005. [Google Scholar] [CrossRef]
  33. Seselj, N.; Engelbrekt, C.; Zhang, J. Graphene-supported platinum catalysts for fuel cells. Sci. Bull. 2015, 60, 864–876. [Google Scholar] [CrossRef] [Green Version]
  34. Fuente, A.M.; Pulgar, G.; González, F.; Pesquera, C.; Blanco, C. Activated carbon supported Pt catalysts: Effect of support texture and metal precursor on activity of acetone hydrogenation. Appl. Catal. A-Gen. 2001, 208, 35–46. [Google Scholar] [CrossRef]
  35. Román-Martínez, M.C.; Cazorla-Amorós, D.; Linares-Solano, A.; de Lecea, C.S.-M. Carbon dioxide hydrogenation catalyzed by alkaline earth- and platinum-based catalysts supported on carbon. Appl. Catal. A-Gen. 1994, 116, 187–204. [Google Scholar] [CrossRef]
  36. Du, J.-P.; Song, C.; Song, J.-L.; Zhao, J.-H.; Zhu, Z.-P. Cyclohexane dehydrogenation over the platinum catalysts supported on carbon nanomaterials. J. Fuel Chem. Technol. 2009, 37, 468–472. [Google Scholar] [CrossRef]
  37. Arevalo-Bastante, A.; Álvarez-Montero, M.A.; Bedia, J.; Gómez-Sainero, L.M.; Rodriguez, J.J. Gas-phase hydrodechlorination of mixtures of chloromethanes with activated carbon-supported platinum catalysts. Appl. Catal. B-Environ. 2015, 179, 551–557. [Google Scholar] [CrossRef] [Green Version]
  38. Auer, E.; Freund, A.; Pietsch, J.; Tacke, T. Carbons as supports for industrial precious metal catalysts. Appl. Catal. A-Gen. 1998, 173, 259–271. [Google Scholar] [CrossRef]
  39. Shelef, M.; Graham, G.W. Why Rhodium in Automotive Three-Way Catalysts? Catal. Rev. 2006, 36, 433–457. [Google Scholar] [CrossRef]
  40. Trzeciak, A.M.; Ziółkowski, J.J.; Jaworska-Galas, Z.; Migta, W.; Wrzyszcz, J. Homogeneous and alumina supported rhodium complex catalysed hydrogenation. J. Mol. Catal. 1994, 88, 13–21. [Google Scholar] [CrossRef]
  41. Alini, S.; Bottino, A.; Capannelli, G.; Carbone, R.; Comite, A.; Vitulli, G. The catalytic hydrogenation of adiponitrile to hexamethylenediamine over a rhodium/alumina catalyst in a three phase slurry reactor. J. Mol. Catal. A-Chem. 2003, 206, 363–370. [Google Scholar] [CrossRef]
  42. Hebben, N.; Diehm, C.; Deutschmann, O. Catalytic partial oxidation of ethanol on alumina-supported rhodium catalysts: An experimental study. Appl. Catal. A-Gen. 2010, 388, 225–231. [Google Scholar] [CrossRef]
  43. Hung, C.M. Characterization and performance of Pt-Pd-Rh cordierite monolith catalyst for selectivity catalytic oxidation of ammonia. J. Hazard. Mater. 2010, 180, 561–565. [Google Scholar] [CrossRef] [PubMed]
  44. Zapf, R.; Thiele, R.; Wichert, M.; O’Connell, M.; Ziogas, A.; Kolb, G. Application of rhodium nanoparticles for steam reforming of propane in microchannels. Catal. Commun. 2013, 41, 140–145. [Google Scholar] [CrossRef]
  45. Choi, K.; Joo, J.M.; Lee, C. Rhodium-catalyzed tandem addition–cyclization of alkynylimines. Tetrahedron 2015, 71, 5910–5917. [Google Scholar] [CrossRef]
  46. Zhang, Q.; Mixdorf, J.C.; Reynders, G.J.; Nguyen, H.M. Rhodium-catalyzed benzylic fluorination of trichloroacetimidates. Tetrahedron 2015, 71, 5932–5938. [Google Scholar] [CrossRef]
  47. Özhava, D.; Özkar, S. Nanoalumina-supported rhodium(0) nanoparticles as catalyst in hydrogen generation from the methanolysis of ammonia borane. Mol. Catal. 2017, 439, 50–59. [Google Scholar] [CrossRef]
  48. Kiss, B.; Manning, T.D.; Hesp, D.; Didier, C.; Taylor, A.; Pickup, D.M.; Chadwick, A.V.; Allison, H.E.; Dhanak, V.R.; Claridge, J.B.; et al. Nano-structured rhodium doped SrTiO3–Visible light activated photocatalyst for water decontamination. Appl. Catal. B-Environ. 2017, 206, 547–555. [Google Scholar] [CrossRef]
  49. Coq, B.; Figueras, F. Bimetallic palladium catalysts: Influence of the co-metal on the catalyst performance. J. Mol. Catal. A-Chem. 2001, 173, 117–134. [Google Scholar] [CrossRef]
  50. Hungría, A.B.; Iglesias-Juez, A.; Martínez-Arias, A.; Fernández-García, M.; Anderson, J.A.; Conesa, J.C.; Soria, J. Effects of Copper on the Catalytic Properties of Bimetallic Pd–Cu/(Ce,Zr)Ox/Al2O3 and Pd–Cu/(Ce,Zr)Ox Catalysts for CO and NO Elimination. J. Catal. 2002, 206, 281–294. [Google Scholar] [CrossRef]
  51. Fernández-García, M.; Martínez-Arias, A.; Iglesias-Juez, A.; Hungría, A.B.; Anderson, J.A.; Conesa, J.C.; Soria, J. Behavior of bimetallic Pd-Cr/Al2O3 and Pd-Cr/(Ce,Zr)Ox/Al2O3 catalysts for CO and NO elimination. J. Catal. 2003, 214, 220–233. [Google Scholar] [CrossRef]
  52. Ershov, B.G.; Anan’ev, A.V.; Abkhalimov, E.V.; Kochubei, D.I.; Kriventsov, V.V.; Plyasova, L.M.; Molina, I.Y.; Kozitsyna, N.Y.; Nefedov, S.E.; Vargaftik, M.N.; et al. Bimetallic Pd-M (M = Co, Ni, Zn, Ag) nanoparticles containing transition metals: Synthesis, characterization, and catalytic performance. Nanotechnol. Russ. 2011, 6, 323–329. [Google Scholar] [CrossRef]
  53. Hinokuma, S.; Katsuhara, Y.; Ando, E.; Ikeue, K.; Machida, M. PdFe/CeO2 bimetal catalysts prepared by dual arc-plasma deposition. Catal. Today 2013, 201, 92–97. [Google Scholar] [CrossRef]
  54. Hilli, Y.; Kinnunen, N.M.; Suvanto, M.; Savimäki, A.; Kallinen, K.; Pakkanen, T.A. Preparation and characterization of Pd–Ni bimetallic catalysts for CO and C3H6 oxidation under stoichiometric conditions. Appl. Catal. A-Gen. 2015, 497, 85–95. [Google Scholar] [CrossRef]
  55. Shan, S.; Petkov, V.; Prasai, B.; Wu, J.; Joseph, P.; Skeete, Z.; Kim, E.; Mott, D.; Malis, O.; Luo, J.; et al. Catalytic activity of bimetallic catalysts highly sensitive to the atomic composition and phase structure at the nanoscale. Nanoscale 2015, 7, 18936–18948. [Google Scholar] [CrossRef] [PubMed]
  56. Xu, Z.F.; Wang, Y.X. Effects of Alloyed Metal on the Catalysis Activity of Pt for Ethanol Partial Oxidation: Adsorption and Dehydrogenation on Pt3M (M = Pt, Ru, Sn, Re, Rh, and Pd). J. Phys. Chem. C 2011, 115, 20565–20571. [Google Scholar] [CrossRef] [Green Version]
  57. Shubin, Y.V.; Vedyagin, A.A.; Plyusnin, P.E.; Kirilovich, A.K.; Kenzhin, R.M.; Stoyanovskii, V.O.; Korenev, S.V. The peculiarities of Au–Pt alloy nanoparticles formation during the decomposition of double complex salts. J. Alloys Compnd. 2018, 740, 935–940. [Google Scholar] [CrossRef]
  58. Nunan, J.G.; Williamson, W.B.; Robota, H.J.; Henk, M.G. Impact of Pt-Rh and Pd-Rh Interactions on Performance of Bimetal Catalysts. SAE Tech. Paper 1995, 950258. [Google Scholar] [CrossRef]
  59. Araya, P.; Díaz, V. Synergism in the reaction of CO with O2 on bimetallic Rh-Pd catalysts supported on silica. J. Chem. Soc. Faraday Trans. 1997, 93, 3887–3891. [Google Scholar] [CrossRef]
  60. Wu, X.; Xu, L.; Weng, D. The thermal stability and catalytic performance of Ce-Zr promoted Rh-Pd/γ-Al2O3 automotive catalysts. Appl. Surf. Sci. 2004, 221, 375–383. [Google Scholar] [CrossRef]
  61. De Sarkar, A.; Khanra, B. CO oxidation and NO reduction over supported Pt-Rh and Pd-Rh nanocatalysts: A comparative study. J. Mol. Catal. A-Chem. 2005, 229, 25–29. [Google Scholar] [CrossRef]
  62. Hangas, J.; Chen, A.E. Comparative Analytical Study of Two Pt–Rh Three-way Catalysts. Catal. Lett. 2006, 108, 103–111. [Google Scholar] [CrossRef]
  63. Renzas, J.R.; Huang, W.; Zhang, Y.; Grass, M.E.; Somorjai, G.A. Rh1−xPdx Nanoparticle Composition Dependence in CO Oxidation by NO. Catal. Lett. 2010, 141, 235–241. [Google Scholar] [CrossRef] [Green Version]
  64. Büchel, R.; Pratsinis, S.E.; Baiker, A. Mono-and bimetallic Rh and Pt NSR-catalysts prepared by controlled deposition of noble metals on support or storage component. Appl. Catal. B-Environ. 2012, 113–114, 160–171. [Google Scholar] [CrossRef] [Green Version]
  65. Vedyagin, A.A.; Volodin, A.M.; Stoyanovskii, V.O.; Kenzhin, R.M.; Slavinskaya, E.M.; Mishakov, I.V.; Plyusnin, P.E.; Shubin, Y.V. Stabilization of active sites in alloyed Pd–Rh catalysts on γ-Al2O3 support. Catal. Today 2014, 238, 80–86. [Google Scholar] [CrossRef]
  66. Zhan, Z.; Song, L.; Liu, X.; Jiao, J.; Li, J.; He, H. Effects of synthesis methods on the performance of Pt + Rh/Ce0.6Zr0.4O2 three-way catalysts. J. Environ. Sci. 2014, 26, 683–693. [Google Scholar] [CrossRef]
  67. Shang, H.; Wang, Y.; Cui, Y.; Fang, R.; Hu, W.; Gong, M.; Chen, Y. Catalytic performance of Pt–Rh/CeZrYLa+LaAl with stoichiometric natural gas vehicles emissions. Chinese J. Catal. 2015, 36, 290–298. [Google Scholar] [CrossRef]
  68. Vedyagin, A.A.; Plyusnin, P.E.; Rybinskaya, A.A.; Shubin, Y.V.; Mishakov, I.V.; Korenev, S.V. Synthesis and study of Pd-Rh alloy nanoparticles and alumina-supported low-content Pd-Rh catalysts for CO oxidation. Mater. Res. Bull. 2018, 102, 196–202. [Google Scholar] [CrossRef]
  69. Shubin, Y.V.; Plyusnin, P.E.; Korenev, S.V. Determination of the equilibrium miscibility gap in the Pd–Rh alloy system using metal nanopowders obtained by decomposition of coordination compounds. J. Alloys Compnd. 2015, 622, 1055–1060. [Google Scholar] [CrossRef]
  70. Vedyagin, A.A.; Stoyanovskii, V.O.; Plyusnin, P.E.; Shubin, Y.V.; Slavinskaya, E.M.; Mishakov, I.V. Effect of metal ratio in alumina-supported Pd-Rh nanoalloys on its performance in three way catalysis. J. Alloys Compnd. 2018, 749, 155–162. [Google Scholar] [CrossRef]
  71. Kostin, G.A.; Plyusnin, P.E.; Filatov, E.Y.; Kuratieva, N.V.; Vedyagin, A.A.; Kal’nyi, D.B. Double complex salts [PdL4][RuNO(NO2)4OH] (L = NH3, Py) synthesis, structure and preparation of bimetallic metastable solid solution Pd0.5Ru0.5. Polyhedron 2019, 159, 217–225. [Google Scholar] [CrossRef]
  72. Sakamoto, Y.; Ohira, K.; Kokubu, M.; Flanagan, T.B. Thermodynamic properties for solution of hydrogen in Pd-Pt-Rh ternary alloys. J. Alloys Compnd. 1997, 253, 212–215. [Google Scholar] [CrossRef]
  73. Lukaszewski, M.; Grden, M.; Czerwinski, A. Cyclic voltammetric behavior of Pd-Pt-Rh ternary alloys. J. Solid State Electr. 2005, 9, 1–9. [Google Scholar] [CrossRef]
  74. Chen, Y.; Liao, S.Z.; Deng, H.Q. The Rh influence on the surface distribution of the ternary alloy Pt-Pd-Rh. Appl. Surf. Sci. 2007, 253, 6074–6079. [Google Scholar] [CrossRef]
  75. Luyten, J.; Creemers, C. Surface segregation in ternary Pt-Pd-Rh alloys studied with Monte Carlo simulations and the modified embedded atom method. Surf. Sci. 2008, 602, 2491–2495. [Google Scholar] [CrossRef]
  76. Bhagiyalakshmi, M.; Anuradha, R.; Park, S.D.; Park, T.S.; Cha, W.S.; Jang, H.T. Effect of Bimetallic Pt-Rh and Trimetallic Pt-Pd-Rh Catalysts for Low Temperature Catalytic Combustion of Methane. B. Korean Chem. Soc. 2010, 31, 120–124. [Google Scholar] [CrossRef] [Green Version]
  77. Hung, C.M. Cordierite-supported Pt-Pd-Rh ternary composite for selective catalytic oxidation of ammonia. Powder Technol. 2010, 200, 78–83. [Google Scholar] [CrossRef]
  78. Bagot, P.A.J.; Kruska, K.; Haley, D.; Carrier, X.; Marceau, E.; Moody, M.P.; Smith, G.D.W. Oxidation and Surface Segregation Behavior of a Pt-Pd-Rh Alloy Catalyst. J. Phys. Chem. C 2014, 118, 26130–26138. [Google Scholar] [CrossRef]
  79. Sarker, M.S.I.; Nakamura, T.; Sato, S. Composition-controlled ternary Rh-Pd-Pt solid-solution alloy nanoparticles by laser irradiation of mixed solution of metallic ions. J. Mater. Res. 2014, 29, 856–864. [Google Scholar] [CrossRef]
  80. Liu, T.D.; Xu, L.Y.; Shao, G.F.; Tu, N.N.; Tao, J.P.; Wen, Y.H. Structural optimization of Pt-Pd-Rh trimetallic nanoparticles using improved genetic algorithm. J. Alloys Compnd. 2016, 663, 466–473. [Google Scholar] [CrossRef]
  81. Liu, X.; Han, Y.Q.; Jia, H.S. Pt-Rh-Pd Alloy Group Gauze Catalysts Used for Ammonia Oxidation. Rare Met. Mater. Eng. 2017, 46, 339–343. [Google Scholar]
  82. Vedyagin, A.A.; Volodin, A.M.; Stoyanovskii, V.O.; Mishakov, I.V.; Medvedev, D.A.; Noskov, A.S. Characterization of active sites of Pd/Al2O3 model catalysts with low Pd content by luminescence, EPR and ethane hydrogenolysis. Appl. Catal. B-Environ. 2011, 103, 397–403. [Google Scholar] [CrossRef]
  83. Stoyanovskii, V.O.; Vedyagin, A.A.; Aleshina, G.I.; Volodin, A.M.; Noskov, A.S. Characterization of Rh/Al2O3 catalysts after calcination at high temperatures under oxidizing conditions by luminescence spectroscopy and catalytic hydrogenolysis. Appl. Catal. B-Environ. 2009, 90, 141–146. [Google Scholar] [CrossRef]
  84. Chen, X.; Cheng, Y.; Seo, C.Y.; Schwank, J.W.; McCabe, R.W. Aging, re-dispersion, and catalytic oxidation characteristics of model Pd/Al2O3 automotive three-way catalysts. Appl. Catal. B-Environ. 2015, 163, 499–509. [Google Scholar] [CrossRef]
  85. Morgan, K.; Goguet, A.; Hardacre, C. Metal Redispersion Strategies for Recycling of Supported Metal Catalysts: A Perspective. Acs Catal. 2015, 5, 3430–3445. [Google Scholar] [CrossRef] [Green Version]
  86. Lupescu, J.A.; Schwank, J.W.; Fisher, G.B.; Chen, X.; Peczonczyk, S.L.; Drews, A.R. Pd model catalysts: Effect of aging duration on lean redispersion. Appl. Catal. B-Environ. 2016, 185, 189–202. [Google Scholar] [CrossRef] [Green Version]
  87. Lupescu, J.A.; Schwank, J.W.; Fisher, G.B.; Hangas, J.; Peczonczyk, S.L.; Paxton, W.A. Pd model catalysts: Effect of air pulse length during redox aging on Pd redispersion. Appl. Catal. B-Environ. 2018, 223, 76–90. [Google Scholar] [CrossRef]
  88. Seo, C.Y.; Chen, X.Y.; Sun, K.; Allard, L.F.; Fisher, G.B.; Schwank, J.W. Palladium redispersion at high temperature within the Pd@SiO2 core@shell structure. Catal. Commun. 2018, 108, 73–76. [Google Scholar] [CrossRef]
  89. Fernandes, D.M.; Scofield, C.F.; Neto, A.A.; Cardoso, M.J.B.; Zotin, F.M.Z. Thermal deactivation of Pt/Rh commercial automotive catalysts. Chem. Eng. J. 2010, 160, 85–92. [Google Scholar] [CrossRef]
  90. Vedyagin, A.A.; Stoyanovskii, V.O.; Kenzhin, R.M.; Slavinskaya, E.M.; Plyusnin, P.E.; Shubin, Y.V. Purification of gasoline exhaust gases using bimetallic Pd–Rh/δ-Al2O3 catalysts. Reac. Kinet. Mech. Catal. 2019, 127, 137–148. [Google Scholar] [CrossRef]
  91. Kraus, W.; Nolze, G. POWDER CELL—A program for the representation and manipulation of crystal structures and calculation of the resulting X-ray powder patterns. J. Appl. Crystallogr. 1996, 29, 301–303. [Google Scholar] [CrossRef]
  92. Krumm, S. An Interactive Windows Program for Profile Fitting and Size/Strain Analysis. Mater. Sci. Forum 1996, 228, 183–190. [Google Scholar] [CrossRef]
  93. Stoyanovskii, V.O.; Vedyagin, A.A.; Volodin, A.M.; Kenzhin, R.M.; Slavinskaya, E.M.; Plyusnin, P.E.; Shubin, Y.V. Optical Spectroscopy Methods in the Estimation of the Thermal Stability of Bimetallic Pd–Rh/Al2O3 Three-Way Catalysts. Top. Catal. 2018, 62, 296–304. [Google Scholar] [CrossRef]
  94. Vedyagin, A.A.; Gavrilov, M.S.; Volodin, A.M.; Stoyanovskii, V.O.; Slavinskaya, E.M.; Mishakov, I.V.; Shubin, Y.V. Catalytic Purification of Exhaust Gases Over Pd–Rh Alloy Catalysts. Top. Catal. 2013, 56, 1008–1014. [Google Scholar] [CrossRef]
  95. Vedyagin, A.A.; Volodin, A.M.; Kenzhin, R.M.; Stoyanovskii, V.O.; Shubin, Y.V.; Plyusnin, P.E.; Mishakov, I.V. Effect of metal-metal and metal-support interaction on activity and stability of Pd-Rh/alumina in CO oxidation. Catal. Today 2017, 293-294, 73–81. [Google Scholar] [CrossRef]
  96. Vedyagin, A.A.; Shubin, Y.V.; Kenzhin, R.M.; Plyusnin, P.E.; Stoyanovskii, V.O.; Volodin, A.M. Prospect of Using Nanoalloys of Partly Miscible Rhodium and Palladium in Three-Way Catalysis. Top. Catal. 2018, 62, 305–314. [Google Scholar] [CrossRef]
  97. Pd-Pt Binary Phase Diagram 0-100, at. Pd-Pt Binary Phase Diagram 0-100 at.% Pt: Datasheet from "PAULING FILE Multinaries Edition—2012" in SpringerMaterials; Villars2016:sm_isp_c_0979992; Springer: Berlin/Heidelberg, Germany; Material Phases Data System (MPDS): Vitznau, Switzerland; National Institute for Materials Science (NIMS): Tsukuba, Japan.
  98. Pt-Rh Binary Phase Diagram 0-100, at. Pt-Rh Binary Phase Diagram 0-100 at.% Rh: Datasheet from "PAULING FILE Multinaries Edition—2012" in SpringerMaterials; Villars2016:sm_isp_c_0979899; Springer: Berlin/Heidelberg, Germany; Material Phases Data System (MPDS): Vitznau, Switzerland; National Institute for Materials Science (NIMS): Tsukuba, Japan.
  99. Bharadwaj, S.R.; Tripathi, S.N. The Pd-Pt (palladium-platinum) system. J. Alloy Phase Diagr. 1990, 6, 118–121. [Google Scholar]
  100. Bharadwaj, S.R.; Kerkar, A.S.; Tripathi, S.N.; Dharwadkar, S.R. The palladium-platinum phase diagram. J. Less Common Met. 1991, 169, 167–172. [Google Scholar] [CrossRef]
  101. Shubin, Y.V.; Korenev, S.V.; Sharafutdinov, M.R. High-temperature X-ray diffraction study of thermolysis of the double complex salt [Rh(NH3)5Cl][PtCl4]. Russ. Chem. Bull. 2006, 55, 1109–1113. [Google Scholar] [CrossRef]
  102. Zhao, J.C.; Jackson, M.R.; Peluso, L.A.; Brewer, L.N. A diffusion-multiple approach for mapping phase diagrams, hardness, and elastic modulus. JOM 2002, 54, 42–45. [Google Scholar] [CrossRef]
  103. Zhao, J.C. Reliability of the diffusion-multiple approach for phase diagram mapping. J. Mater. Sci. 2004, 39, 3913–3925. [Google Scholar] [CrossRef]
  104. Luyten, J.; De Keyzer, J.; Wollants, P.; Creemers, C. Construction of modified embedded atom method potentials for the study of the bulk phase behaviour in binary Pt-Rh, Pt-Pd, Pd-Rh and ternary Pt-Pd-Rh alloys. Calphad 2009, 33, 370–376. [Google Scholar] [CrossRef]
  105. Powder Diffraction File PDF-2; International Centre for Diffraction Data (ICDD): Newtown Square, PA, USA, 2009.
  106. Tripathi, S.N.; Bharadwqj, S.R. The Pd-Rh (Palladium-Rhodium) system. J. Phase Equilibria 1994, 15, 208–212. [Google Scholar] [CrossRef]
  107. Koffyberg, F.P. Optical bandgaps and electron affinities of semiconducting Rh2O3(I) and Rh2O3(III). J. Phys. Chem. Solids 1992, 53, 1285–1288. [Google Scholar] [CrossRef]
  108. Aita, C.R. Optical behavior of sputter-deposited platinum-oxide films. J. Appl. Phys. 1985, 58, 3169–3173. [Google Scholar] [CrossRef]
  109. Zhensheng, J.; Chanjuan, X.; Qingmei, Z.; Feng, Y.; Jiazheng, Z.; Jinzhen, X. Catalytic behavior of nanoparticle α-PtO2 for ethanol oxidation. J. Mol. Catal. A-Chem. 2003, 191, 61–66. [Google Scholar] [CrossRef]
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Figure 1. Infrared spectra (a) and experimental XRD patterns (b) of the prepared complex compounds. The calculated pattern of [RhEn3]2[Pt(NO2)4]3 is given for comparison.
Figure 1. Infrared spectra (a) and experimental XRD patterns (b) of the prepared complex compounds. The calculated pattern of [RhEn3]2[Pt(NO2)4]3 is given for comparison.
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Figure 2. The thermal analysis curves obtained in a reductive medium at a ramping rate of 10 °C/min: (a) TG, DTG, and DTA for the [RhEn3]2[Pd0.5Pt0.5(NO2)4]3 salt and (b) TG curves for the solid solutions [RhEn3]2[PdxPt1−x(NO2)4]3.
Figure 2. The thermal analysis curves obtained in a reductive medium at a ramping rate of 10 °C/min: (a) TG, DTG, and DTA for the [RhEn3]2[Pd0.5Pt0.5(NO2)4]3 salt and (b) TG curves for the solid solutions [RhEn3]2[PdxPt1−x(NO2)4]3.
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Figure 3. HR TEM images and EDX spectra of the as-prepared nanoalloys. (a) Rh2Pd3; (b) Rh2(Pd0.50Pt0.50)3; and (c) Rh2Pt3.
Figure 3. HR TEM images and EDX spectra of the as-prepared nanoalloys. (a) Rh2Pd3; (b) Rh2(Pd0.50Pt0.50)3; and (c) Rh2Pt3.
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Figure 5. The XRD patterns of the prepared nanoalloys within 2θ ranges of 35–90 ° (a) and 123–133 ° (b).
Figure 5. The XRD patterns of the prepared nanoalloys within 2θ ranges of 35–90 ° (a) and 123–133 ° (b).
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Figure 6. Dependencies of the lattice parameters of the Rh-Pt and Rh-Pd nanoalloys on their composition.
Figure 6. Dependencies of the lattice parameters of the Rh-Pt and Rh-Pd nanoalloys on their composition.
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Figure 7. The temperature dependencies of CO conversion under prompt thermal aging (PTA) conditions for the studied samples: (a) Pt/γ-Al2O3; (b) Rh2Pt3/γ-Al2O3; (c) Rh2(Pd0.25Pt0.75)3/γ-Al2O3; (d) Rh2(Pd0.5Pt0.5)3/γ-Al2O3; and (e) Rh2(Pd0.75Pt0.25)3/γ-Al2O3. The dependencies of the T50 parameter on the run number for the same samples (f).
Figure 7. The temperature dependencies of CO conversion under prompt thermal aging (PTA) conditions for the studied samples: (a) Pt/γ-Al2O3; (b) Rh2Pt3/γ-Al2O3; (c) Rh2(Pd0.25Pt0.75)3/γ-Al2O3; (d) Rh2(Pd0.5Pt0.5)3/γ-Al2O3; and (e) Rh2(Pd0.75Pt0.25)3/γ-Al2O3. The dependencies of the T50 parameter on the run number for the same samples (f).
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Figure 8. The diffuse reflectance UV-vis spectra of the samples Pt/γ-Al2O3, Rh/γ-Al2O3, Rh2Pt3/γ-Al2O3, and Rh+Pt/γ-Al2O3 treated at 400 °C, and sample Pt/γ-Al2O3 additionally calcined in argon at 400 °C. All the spectra are corrected concerning the support.
Figure 8. The diffuse reflectance UV-vis spectra of the samples Pt/γ-Al2O3, Rh/γ-Al2O3, Rh2Pt3/γ-Al2O3, and Rh+Pt/γ-Al2O3 treated at 400 °C, and sample Pt/γ-Al2O3 additionally calcined in argon at 400 °C. All the spectra are corrected concerning the support.
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Figure 9. (a) The diffuse reflectance UV-vis spectra of samples Pt/γ-Al2O3 aged under PTA conditions, treated at 400 °C, and treated at 400 °C after aging under PTA conditions. All the spectra are corrected concerning the support. (b) The charge transfer part of the spectra.
Figure 9. (a) The diffuse reflectance UV-vis spectra of samples Pt/γ-Al2O3 aged under PTA conditions, treated at 400 °C, and treated at 400 °C after aging under PTA conditions. All the spectra are corrected concerning the support. (b) The charge transfer part of the spectra.
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Figure 10. The diffuse reflectance UV-vis spectra of samples Pt/γ-Al2O3, Rh2Pt3/γ-Al2O3, and Rh+Pt/γ-Al2O3 aged at 800 °C and treated at 400 °C. All the spectra are corrected concerning the support.
Figure 10. The diffuse reflectance UV-vis spectra of samples Pt/γ-Al2O3, Rh2Pt3/γ-Al2O3, and Rh+Pt/γ-Al2O3 aged at 800 °C and treated at 400 °C. All the spectra are corrected concerning the support.
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Figure 11. The diffuse reflectance UV-vis spectra of samples Rh2(Pd0.25Pt0.75)3/γ-Al2O3, Rh2(Pd0.5Pt0.5)3/γ-Al2O3, and Rh2(Pd0.75Pt0.25)3/γ-Al2O3 treated at 400 °C: (a) initial and (b) aged at 800 °C under PTA conditions. All the spectra are corrected concerning the support.
Figure 11. The diffuse reflectance UV-vis spectra of samples Rh2(Pd0.25Pt0.75)3/γ-Al2O3, Rh2(Pd0.5Pt0.5)3/γ-Al2O3, and Rh2(Pd0.75Pt0.25)3/γ-Al2O3 treated at 400 °C: (a) initial and (b) aged at 800 °C under PTA conditions. All the spectra are corrected concerning the support.
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Table
Table 1. Elemental composition of the double complex salts.
Table 1. Elemental composition of the double complex salts.
PrecursorContent (Measured/Calculated), %
CNHPtRhPd
[RhEn3]2[Pd(NO2)4]39.5/10.0220.4/23.383.1/3.37-14.1/14.3221.2/22.21
[RhEn3]2[Pt(NO2)4]38.4/8.4619.6/19.732.8/2.8435.0/34.3512.0/12.08-
[RhEn3]2[Pd0.5Pt0.5(NO2)4]39.0/9.1821.3/21.403.0/3.0819.3/18.6313.3/13.109.5/10.16
Table
Table 2. The oscillation frequencies in the infrared spectra of the prepared complex compounds.
Table 2. The oscillation frequencies in the infrared spectra of the prepared complex compounds.
Compoundνs(NH)ν(CH)δ(NH2)νa(NO2)ν(CN)δ(ONO)
[RhEn3]2[Pd(NO2)4]33271
3237
3153		296515811428
1390
1327
1299		1050823
[RhEn3]2[Pt(NO2)4]33278
3234
3161		29621597
1582
1146		1432
1394
1331		1049827
[RhEn3]2[Pd0.75Pt0.25(NO2)4]33271
3237
3153		29641597
1581
1145		1428
1391
1328		1050824
[RhEn3]2[Pd0.5Pt0.5(NO2)4]33273
3237
3147		29641596
1581
1145		1429
1393
1330		1050826
[RhEn3]2[Pd0.25Pt0.75(NO2)4]33275
3236
3148		29631597
1582
1146		1431
1394
1332		1050827
Table
Table 3. Content of metals in the composition of the prepared complex salts according to the thermal analysis results.
Table 3. Content of metals in the composition of the prepared complex salts according to the thermal analysis results.
CompoundMeasuredCalculated
[RhEn3]2[Pd(NO2)4]336.8%36.53%
[RhEn3]2[Pd0.75Pt0.25(NO2)4]339.2%39.33%
[RhEn3]2[Pd0.5Pt0.5(NO2)4]341.7%41.89%
[RhEn3]2[Pd0.25Pt0.75(NO2)4]344.3%44.26%
[RhEn3]2[Pt(NO2)4]346.2%46.43%
Table
Table 5. Content of metals in the composition of the alumina-supported catalysts according to the ED XRF results.
Table 5. Content of metals in the composition of the alumina-supported catalysts according to the ED XRF results.
SampleContent (Measured/Calculated), %
RhPdPt
Rh2Pt3/Al2O30.05/0.051-0.15/0.149
Rh2Pd3/Al2O30.08/0.0760.12/0.119-
Rh2(Pd0.25Pt0.75)3/Al2O30.05/0.0570.03/0.0220.11/0.121
Rh2(Pd0.5Pt0.5)3/Al2O30.05/0.0620.05/0.0480.10/0.089
Rh2(Pd0.75Pt0.25)3/Al2O30.07/0.0690.08/0.0810.06/0.049
Pt/Al2O3--0.16/0.15
Pd/Al2O3-0.11/0.119-
Table
Table 6. The values of the band gap (Eg) for the studied samples in the initial state and after aging under PTA conditions. All the samples were treated on air at 400 °C before the characterization.
Table 6. The values of the band gap (Eg) for the studied samples in the initial state and after aging under PTA conditions. All the samples were treated on air at 400 °C before the characterization.
SampleEg, eV
InitialAged at 800 °C
Pt/γ-Al2O32.621.65
Rh2Pt3/γ-Al2O32.471.97
Rh+Pt/γ-Al2O32.342.01
Rh2(Pd0.25Pt0.75)3/γ-Al2O32.472.08
Rh2(Pd0. 5Pt0.5)3/γ-Al2O32.442.17
Rh2(Pd0.75Pt0.25)3/γ-Al2O32.432.30

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Vedyagin, A.A.; Shubin, Y.V.; Kenzhin, R.M.; Plyusnin, P.E.; Stoyanovskii, V.O. The Attractiveness of the Ternary Rh-Pd-Pt Alloys for CO Oxidation Process. Processes 2020, 8, 928. https://doi.org/10.3390/pr8080928

AMA Style

Vedyagin AA, Shubin YV, Kenzhin RM, Plyusnin PE, Stoyanovskii VO. The Attractiveness of the Ternary Rh-Pd-Pt Alloys for CO Oxidation Process. Processes. 2020; 8(8):928. https://doi.org/10.3390/pr8080928

Chicago/Turabian Style

Vedyagin, Aleksey A., Yury V. Shubin, Roman M. Kenzhin, Pavel E. Plyusnin, and Vladimir O. Stoyanovskii. 2020. "The Attractiveness of the Ternary Rh-Pd-Pt Alloys for CO Oxidation Process" Processes 8, no. 8: 928. https://doi.org/10.3390/pr8080928

APA Style

Vedyagin, A. A., Shubin, Y. V., Kenzhin, R. M., Plyusnin, P. E., & Stoyanovskii, V. O. (2020). The Attractiveness of the Ternary Rh-Pd-Pt Alloys for CO Oxidation Process. Processes, 8(8), 928. https://doi.org/10.3390/pr8080928

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