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Article

Insights into Contribution of Active Ceria Supports to Pt-Based Catalysts: Doping Effect (Zr; Pr; Tb) on Catalytic Properties for Glycerol Selective Oxidation

by
Matías G. Rinaudo
1,*,
Maria del Pilar Yeste
2,
Hilario Vidal
2,
José M. Gatica
2,
Luis E. Cadús
1 and
Maria R. Morales
1
1
Instituto de Investigaciones en Tecnología Química (INTEQUI-CONICET), Facultad de Química Bioquímica y Farmacia, Universidad Nacional de San Luis (UNSL), Almirante Brown 1455, Capital, San Luis 5700, Argentina
2
Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica y Química Inorgánica, Instituto de Microscopía Electrónica y Materiales (IMEYMAT), Universidad de Cádiz, 11510 Puerto Real, Spain
*
Author to whom correspondence should be addressed.
Inorganics 2025, 13(2), 32; https://doi.org/10.3390/inorganics13020032
Submission received: 20 December 2024 / Revised: 13 January 2025 / Accepted: 21 January 2025 / Published: 22 January 2025
(This article belongs to the Special Issue Transition Metal Catalysts: Design, Synthesis and Applications)
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Versions Notes

Abstract

:
How important is the support during the rational design of a catalyst? Herein, doped ceria (Zr; Pr and Tb) was used as an active support to prepare Pt catalysts (0.5 wt%) for glycerol selective oxidation. A thorough characterization of achieved catalytic systems showed that the nature of doping elements led to different physicochemical properties. The presence of surface Pr3+ and Tb3+ not only increased oxygen vacancies but also electron mobility, modifying the oxidation state of platinum particles. The redox properties of the catalyst were also affected, achieving a close interaction between the support and metal particles even in the form of Pt-O-Pr(Tb) solid solutions. Furthermore, the combination of medium-sized metal particle dispersion, strong metal–support interaction and a synergy between the amount of oxygen vacancies and Pt0, observed in the Pt/CeTb catalyst, led to a high turnover frequency (TOF) and increased selectivity to glyceric acid. Thus, the present study reveals how a simple structural modification of active supports, such as cerium oxide, by means of doping elements is capable of improving the catalytic performance during glycerol selective oxidation, avoiding the cumbersome methods of synthesis and activation treatments.

Graphical Abstract

1. Introduction

It is well known that the performance of supported catalysts can be enhanced by regulating the structure, surface properties and metal–support interactions [1,2,3,4,5]. In the case of metal active sites, some strategies include a good control of geometry, metal particle sizes and surface oxidation state, while tuning surface and bulk composition and defects (such as oxygen vacancies) present in the support could also determine the final behavior of catalysts during a reaction [1,2,4,5]. In this context, the selection of a suitable support could be of paramount importance in order to improve efficiency [6,7,8]. Cerium oxide is a widely used ‘active’ support due to its thermal and mechanical stability, oxygen storage capacity (OSC) and redox properties, provided by its reversible oxidation states between Ce3+ and Ce4+, that encourage its use as an active component, a support or a promoter [9,10]. Furthermore, cerium oxide (or ceria) has the ability to tolerate a high degree of defects and atomic disorder within its structure, where Ce4+ ions present in the fluorite-like lattice could be replaced by doping with other cations, producing mixed oxides with boosted properties [1,3]. These doped materials could not only increase the intrinsic redox properties and OSC of ceria but also control surface physicochemical properties, affecting metal anchoring/dispersion, the adsorption of reactants and electron mobility on the surface [1,3]. Among different possibilities, chemical doping with non-reducible zirconium cations (Zr4+) has been widely studied during the last 20 years due to the improvements in redox properties achieved after introducing these smaller cations within cerium oxide [3,11,12]. Moreover, structural modifications include elements known as rare earths such as praseodymium (Pr) and terbium (Tb), which offer the coexistence of different oxidation states (e.g., Pr3+ and Pr4+), increasing the number of oxygen vacancies and the oxygen diffusion rate, which are of great interest for oxidation reactions [3,6,13,14]. In particular, the formation of solid solutions could promote an increase in the number of active surface oxygen species, facilitating the initial step of deprotonation for alcohol oxidation [3,7,12,15,16]. Additionally, platinum (Pt) catalysts supported on metal oxides have been extensively studied for gas-phase oxidation reactions, since this metal has a low number of vacant d-orbitals (a feature of VIII group metals) that are capable of accepting electrons from reactants for surface adsorption [16,17,18]. Some authors [6,19] have demonstrated that the structural and electronic properties of Pt/CeO2 catalytic system can be modified by tailoring the physicochemical features of ceria, thereby enhancing its catalytic behavior [3,5,6,18]. Furthermore, they have shown that this system is highly active when platinum particles are small, well dispersed and partially oxidized, while metal–ceria synergy could prevent sintering and lixiviation in liquid-phase reactions [3,10,18,20,21].
Since the effect of dopants (Zr; Pr and Tb) on the physicochemical (catalytic) properties of active ceria supports and Pt-based catalysts for glycerol selective oxidation has not been studied yet, the purpose of this study is to shed light on this topic. An in-depth characterization of the catalytic systems was also performed to gain insight into the extent and outcomes of achieved features.

2. Results and Discussion

2.1. Catalysts’ Characterization

Powder X-ray Diffraction (PXRD) analyses (Figure 1) showed characteristic patterns of the fluorite-type face-centered cubic structure of cerianite (PDF 00-34-0394) in all catalysts [1,10]. No diffraction lines corresponding to platinum species were detected, which could be a consequence of its high dispersion and/or low concentration (0.5 wt%), which is out of the detection limit of the diffractometer [10].
Doped supports displayed shifts in cerianite diffraction lines (inset Figure 1) and were associated with the incorporation of each element into the CeO2 lattice, provoking its distortion [1,14]. In comparison with the pure CeO2 support, CeZr showed a decrease in the lattice parameter (Table S1) due to the contraction of the CeO2 lattice after the incorporation of smaller Zr4+ cations in places occupied by Ce4+ cations (ionic radius of 0.084 nm vs. 0.097 nm).
On the other hand, CePr showed an increase in the lattice parameter (lattice expansion) that could be attributed to the doping of Pr3+ and/or Pr4+ cations into the ceria structure (ionic radius of 0.112 and 0.099 nm, respectively) [14]. As in the case of CeZr, CeTb also showed a decrease in the lattice parameter due to the incorporation of Tb3+ and/or Tb4+ cations (ionic radius of 0.098 and 0.088 nm, respectively) [22]. The same trend was observed in the case of catalysts (Table 1) with slight differences due to Pt particle addition and thermal treatments applied during synthesis. All of these changes could lead to a promotional effect in terms of oxygen species mobility and reducibility of catalysts, ultimately affecting the catalytic performance. Textural analyses displayed type II with hysteresis and IV(a) physisorption isotherms, according to the IUPAC classification, with Brunauer–Emmet–Teller (BET) specific surface area (SBET) values between 96 and 62 m2 g−1 (Table 1) [23]. These values were slightly lower compared to those of supports (Table S1), due to platinum impregnation followed by drying and calcination, which also affected total pore volume values.
Additionally, the average crystalline sizes between 5 and 8 nm and pore diameters between 7 and 11 nm are high enough to avoid the diffusional drawbacks of big molecules such as glycerol (average molecule size of 0.62 nm) [10,24]. Also, all catalysts exhibited agglomerated particles with a spherical morphology (Figure S1) with average sizes between 1 and 10 µm. Moreover, platinum loadings obtained by Inductively Coupled Plasma–Optical Emission Spectroscopy (ICP-OES) showed values between 0.45 and 0.48 wt% (Table 2), in line with the theoretical value of 0.5 wt%. Even though hydrogen spill-over effects cannot be discarded and H:Pt chemisorption stoichiometry is >1, thus leading to the apparent metal dispersion of > 100%, H2 chemisorption measurements (Table 2) showed high metal dispersions in all catalysts, with average platinum particles estimated between 0.57 and 1.66 nm [25,26,27,28]. It is important to point out that Pt/CeZr and Pt/CePr showed the greatest decrease in SBET values after platinum impregnation compared to respective supports (Table S1) and also the greatest Pt average particle sizes and lowest dispersion, indicating a distinctive metal–support interaction in these catalysts.
The following trend in metal dispersion, i.e., Pt/Ce > Pt/CeTb >> Pt/CePr > Pt/CeZr, was confirmed by High-Angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF-STEM) images and Energy-dispersive X-ray Spectroscopy (EDX) elemental mapping (Figure 2 and Figure S2 and Table 2), showcasing the effect of tailoring the surface chemistry of ceria, in this case by doping, on the capacity of each support to anchor platinum particles regardless of its SBET value [3]. As already mentioned, the particle size values were larger than those obtained by hydrogen chemisorption owing to the spill-over effect in hydrogen chemisorption [25]. Also, X-ray Photoelectron Spectroscopy (XPS) studies were performed to analyze the oxygen vacancies generated by doping and their effect on the elements present on the surface of each catalyst. Ce 3d spectra were deconvoluted into typical Ce 3d3/2 and Ce 3d5/2 doublets assigned to Ce4+ and Ce3+ according to the literature (Figure 3) [1,4,10,29]. Ce3+/(Ce3+ + Ce4+) ratio (Table 3) showed the same value of 0.15 for Pt/Ce and Pt/CeZr and the absence of Zr3+ signals, due to its non-reducible nature, when studying the Zr 3d level for the latter (Figure S3) [19]. On the other hand, Pt/CePr and Pt/CeTb displayed low values of 0.06 and 0.07, respectively, and M3+/(M3+ + M4+) ratio values of 0.39 and 0.52, where M corresponds to Pr or Tb accordingly, indicating the doping of ceria structure with M3+ cations and its presence on the surface of the catalysts (Table 3, Figures S4 and S5) [1,14,30,31]. These results were in line with the greater Oads/(Oads + Olatt) values (around 0.25) obtained from the deconvolution of O 1s level into the lattice oxygen (Olatt) and oxygen adsorbed on oxygen vacancies (Oads) (Table 3 and Figure 3), associated with the oxygen vacancies promoted by doping the support with Pr and Tb [12,14]. The presence of surface Pr3+ and Tb3+ along with oxygen vacancies could benefit surface regeneration due to enhanced charge and/or reactive oxygen mobility during glycerol oxidation, as reported by other authors [4,7,10,15,29]. Moreover, Pt 4f level was deconvoluted into Pt 4f5/2 and Pt 4f7/2 doublets assigned to Pt0 and Ptδ+ to study the surface oxidation state of metal particles (Figure 4) [6,12]. Pt/Ce, Pt/CeZr and Pt/CePr showed similar values of Pt0/(Pt0 + Ptδ+) between 0.21 and 0.27 (Table 3), while Pt/CeTb stood out in the series of catalysts due to a value of 0.40. This difference could be associated with the greater Tb3+ amount found in this catalyst, which could stabilize platinum particles to preserve the metallic oxidation state, along with a strong metal–support interaction sustained by the considerable shifts observed in the binding energies [2,18,19].
Thus, support’s nature and properties have a significant role on metal speciation [2,6]. Additionally, as reported by Zhang et al. [4], the presence of Ce3+(M3+) cations could also adsorb oxygen to form Ce4+(M4+)-O2− with the superoxo radical (O2−), thus enhancing alcohol oxidation.
Next, Hydrogen Temperature Programmed Reduction (H2-TPR) studies were performed to further study metal–support interaction and reducibility of catalysts (Figure 5). Signals observed in the range of 350–500 °C were associated with the reduction of surface CeO2 while incipient signals starting at 600 °C (particularly in the case of Pt/Ce) were attributed to the lattice oxygen reduction from bulk CeO2, as reported by other authors [4,10,32]. The two overlapped reduction signals observed between 200 and 350 °C were linked to a dual contribution from Ptδ+ to form Pt0 and surface ceria closely interacting with platinum (e.g., Pt-O-Ce bonds), since the theoretical value to reduce Pt4+ to Pt0 should be around 52 µmol g−1 and all catalysts displayed values of over 858 µmol g−1 (Figure 5) [5,12,32,33,34]. The fact that both signals were more defined in Pt/Ce and Pt/CeZr could be associated with a weaker metal–support interaction compared to Pt/CePr and Pt/CeTb, where a single and broader signal was observed [5,12,32]. Moreover, the maximum of these signals in Pt/CePr and Pt/CeTb were shifted to higher temperatures, indicating a strong metal–support interaction that hinders the reducibility of present species [14,32]. As reported by Bugrova et al. [32], the absence of low-temperature reduction signals from platinum species confirmed the stabilization of Pt particles on ceria/doped ceria supports and its high dispersion in small clusters, as observed by previous analyses based on STEM-HAADF-EDX and H2 chemisorption. Additionally, the lowest H2 uptakes from overlapped signals (the first value) was obtained for Pt/CeTb, which could be associated with the higher amount of surface Pt0 present in this catalyst. Also, the values corresponding to the contribution of surface ceria reduction (the second value) were higher in the case of Pt/CeTb and Pt/CePr, which could be attributed to the presence of Tb3+ and Pr3+, increasing the reducibility of the all catalysts and in line with Oads amounts found from XPS [12,14]. The distinctive reducibility observed and reactive oxygen species present in these catalysts, due to oxygen vacancies, dopant contribution and the formation of Pt-O-Pr(Tb) solid solution, could have a significant impact on catalytic performance [1,12,32,33,34,35].

2.2. Catalytic Tests

The calculated turnover frequencies (TOFs) [36] for each catalyst revealed greater values for Pt/CeTb and Pt/CePr (225 and 256 h−1, respectively). This behavior was mainly associated with the average size of platinum particles (Table 2) found in both catalysts (8.5 and 8.4 nm, respectively), while a smaller size observed for Pt/Ce (1.6 nm) decreased the TOF value to 35 h−1, and the greater size of Pt/CeZr (9.3 nm) led to a TOF value of 209 h−1. Glycerol conversion and selectivity to products also tended to be related to the physicochemical properties and metal–support interactions achieved (Figure 6). The higher conversion observed for Pt/CePr could be attributed to the synergistic effect between Pt particles and the support, which is responsible of its enhanced reducibility and reactive oxygen species mobility, in line with XPS and H2-TPR results, followed by Pt/CeTb, Pt/CeZr and finally Pt/Ce [1,4]. Moreover, it was interesting to find out that the selectivity to glyceric acid (GA) and the ratio between Pt0/(Pt0 + Ptδ+) and Oads/(Oads + Olatt) values obtained by XPS followed an almost linear trend (Figure 7), except the slight shift in the case of Pt/CeZr.
This evidenced not only the contribution of oxygen vacancies and structural disorder improved by doping but also the metal–support interaction, affecting the surface oxidation state of platinum species [2]. As reported by Ma et al. [3], oxygen vacancies and Lewis basic sites can regulate the electron transfer and thus the electron density of the surface active sites. In this context, a combination of higher Oads and Pt0 on the surface of the catalysts (as in the case of Pt/CeTb and Pt/Ce) could modify the reaction route during glycerol selective oxidation, promoting GA selectivity, and is the most expensive of the achieved products [37]. As reported by Aneggi et al. [19], the formation of a strong Pt-O-Ce(M) complex could also hinder Pt sintering, promoting the migration and redispersion of Pt agglomerates under oxidative conditions. The features observed in Pt/CeTb and Pt/Ce also contributed, in a minor way, to an increase in lactic acid (LA) selectivity (13 and 11%, respectively), following the dehydration pathway of glycerol conversion [7]. In addition, high Oads and M3+ values (as in the case of Pt/CePr and Pt/CeTb) led to higher selectivity to formic acid (FA), and to a lesser extent oxalic acid (OA), which could be a consequence of the overoxidation of formed products (such as lactic acid and glyceric acid) due to the presence of more reactive oxygen species (O vacancies, O2− and OH radicals) and/or enhanced mobility in the presence of surface Pr3+ and Tb3+ [7,10,34,38]. Moreover, low carbon balance values observed indicated that other intermediate products such as tartronic, glycolic and glyoxylic acids could also be obtained, and even a complete oxidation to form CO2 could occur [7,8]. Thus, by controlling the surface chemistry of ceria, both catalytic efficiency and chemoselectivity can be managed for different heterogeneous reactions, such as in the case of glycerol selective oxidation [3,34].

3. Materials and Methods

3.1. Synthesis of Catalysts

Catalysts were prepared by the ultrasound-assisted impregnation of an aqueous solution of H2PtCl6xH2O (Merck, Burlington, ON, Canada) on each commercial support (Rhodia, La Défense, France): Ce (pure cerium oxide); CeZr (15 wt% zirconium); CePr (20 wt% praseodymium) and CeTb (20 wt% terbium) in order to achieve platinum loadings of 0.5 wt% in final catalysts. The obtained solids were dried for 16 h in an oven under vacuum at 70 °C and calcined in a muffle furnace for 4 h under air at 500 °C (10 °C min−1) to remove the rest of the metal precursor. Pt-based catalysts were labeled as Pt/Ce; Pt/CeZr; Pt/CePr and Pt/CeTb.

3.2. Characterization

Powder X-ray Diffraction (PXRD) spectra were recorded in a Rigaku Ultima IV diffractometer (Rigaku, Tokyo, Japan) operated at 20 mA and 30 kV with a Cu Kα (λ = 0.15405 nm) radiation lamp, a step width of 0.02° and a counting time of 2 s.
Nitrogen physisorption studies were performed following the Brunauer–Emmet–Teller (BET) method using N2 adsorption at 77 K in a Micromeritics Gemini V equipment (Micromeritics, Norcross, GA, USA). Samples were previously outgassed overnight at 250 °C under N2.
Scanning Electron Microscopy (SEM) analyses were conducted in a LEO 1450 VP SEM equipment (Carl Zeiss AG, Oberkochen, Germany). Samples were put on aluminum sample holders and sputtered with gold in advance.
The Pt content was quantified in an Inductively Coupled Plasma–Optical Emission Spectroscopy (ICP-OES) IRIS Intrepid HR instrument after the digestion of the catalysts in a mixture of inorganic acids.
High-Angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF-STEM) images were obtained using Talos F200X (Thermo Fisher Scientific, Waltham, MA, USA) at 200 kV of accelerating voltage. Energy-dispersive X-ray Spectroscopy (EDX) maps were collected using a Super X G2 XEDS system (Thermo Fisher Scientific, Waltham, MA, USA) and analyzed by the Velox software.
Hydrogen chemisorption studies were performed in a Micromeritics ASAP 2020C Instrument assuming a H:Pt chemisorption stoichiometric of 1 and following the method of a previous study [25].
X-ray Photoelectron Spectroscopy (XPS) spectra were recorded using XPS SPECS ProvenX-PS (SPECS, Berlin, Germany) with a pressure under 1 × 10−9 mbar during all measurements. Spectra were obtained for the C 1s, O 1s, Ce 3d, Zr 3d, Pr 3d, Tb 4d and Pt 4f regions. C 1s binding energy (284.6 eV) was used as the internal reference to correct peak positions. The XPSPeak 4.1 free software was used for data processing.
Hydrogen Temperature Programmed Reduction (H2-TPR) measurements were conducted in a homemade equipment using a quartz tubular reactor and a TCD detector under the same conditions reported in a previous study [9]. Briefly, catalysts were first pretreated with He (30 mL min−1) at 150 °C for 30 min. Reduction process was performed using a mixture of 5% H2 in N2 (30 mL min−1) from room temperature (once baseline remained constant) to 900 °C at a heating rate of 10 °C min−1 and then kept at this final temperature until H2 consumption signal returned to the starting values. The H2 uptake was measured after calibration by pure N2 pulses with a six-port pulsing valve (a constant loop volume of 0.25 mL), using ideal gasses law and both ambient temperature and pressure of the day and hour of measurement.

3.3. Catalytic Evaluation

Liquid-phase glycerol selective oxidation was performed in a 50 mL steel Parr-type reactor equipped with a pressure gauge, oven and controllers for temperature and agitation. For each test, 20 mL of 0.15 M glycerol (99.7%, Biopack) aqueous solution, sodium hydroxide (≥97.0%, Biopack) to reach a NaOH/glycerol molar ratio of 2 and 200 mg of catalyst were added into the reactor. Temperature was set at 100 °C under 1000 rpm of agitation speed, 1 bar of pure oxygen and 4 h of reaction time.
Reaction products were identified and quantified in a HPLC instrument equipped with an Aminex HPX-87H column (300 × 7.8 mm) and a UV diode array as a detector (Waters, Milford, CT, USA). Operating conditions and external calibration curves used have been reported in a previous study [7].
The conversion of glycerol, selectivity to products and carbon balance were calculated according to the equations reported in the literature [8]. The turnover frequency (TOF) values were calculated using the average Pt particle size from STEM-HAADF (see Supplementary Materials) [36].

4. Conclusions

Even though a high dispersion in nano-sized metal domains is usually considered the dominant factor for a good conversion in most catalysts, the presence of reactive oxygen species on the surface could have a major contribution during glycerol oxidation, facilitating the first step of alcohol deprotonation, oxygen supply and active site regeneration throughout the reaction. In this regard, the intrinsic features of ceria can be promoted by simply doping with rare earths, such as Pr and Tb, increasing surface oxygen vacancies and ion mobility, regulating the adsorption/desorption of reactants and products and even creating new catalytic sites due to the metal–support interaction, which could consequently affect the catalytic performance. Pt/CePr and Pt/CeTb exhibited the highest TOF values, due to the dispersion of medium-sized platinum particles, but only the Pt/CeTb catalyst showed a distinctive Oads-Pt0 synergy and a strong Pt-O-Tb interaction, leading to an increase in LA and mainly GA selectivity, which is the most valuable product of glycerol selective oxidation. Therefore, the boundaries between metal centers and supports play a crucial role in terms of catalytic activity, since smaller particles could be less selective to an expected product. The present study provides insights on the significant contribution of supports when designing a catalytic system, particularly in the case of doped ceria supports for oxidation reactions. In addition to its well-known function as a carrier of metal active particles, it is important to highlight its involvement in metal–support interactions and surface physicochemical properties, which are capable of directing the catalytic performance towards a target reaction product. A focus on the proper selection and modification of the support could prevent the usage of intricated routes of synthesis/activation procedures and high amounts of metal precursors, reducing the costs and increasing the environmental friendliness of the whole catalytic systems.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/inorganics13020032/s1, Figure S1. SEM micrographs (1.5 kx) of catalysts: Pt/Ce (A), Pt/CeZr (B), Pt/CePr (C) and Pt/CeTb (D); Figure S2. STEM-HAADF particle size distribution of catalysts; Figure S3. XPS spectra of Zr 3d of Pt/CeZr catalyst; Figure S4. XPS spectra of Pr 3d of Pt/CePr catalyst; Figure S5. XPS spectra of Tb 4d of Pt/CeTb catalyst; Table S1. Textural properties of commercial supports and TOF calculations.

Author Contributions

Conceptualization, M.G.R., M.R.M. and L.E.C.; investigation, M.G.R., M.R.M., L.E.C., M.d.P.Y., H.V. and J.M.G.; visualization, M.G.R.; writing—original draft, M.G.R.; writing—review, M.G.R., M.R.M., L.E.C., M.d.P.Y., H.V. and J.M.G.; writing—editing, M.G.R.; validation, M.R.M., L.E.C., M.d.P.Y., H.V. and J.M.G.; supervision, L.E.C. and M.R.M.; resources, L.E.C. and M.R.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Universidad Nacional de San Luis (UNSL), Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) and Ministry of Economy and Competitiveness of Spain (Project PID2020-113006-RB-I00) and the Junta de Andalucía (FQM-110 and FQM-169 groups).

Data Availability Statement

Data are contained within the article and Supplementary Materials. Further inquiries can be directed to the corresponding author.

Acknowledgments

Special thanks are given to the Central Services of Investigation on Science and Technology (SCI-CyT) of Cadiz University (UCA) for the access to their installations and equipment.

Conflicts of Interest

The authors declare no conflicts of interest.

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Inorganics 13 00032 g001
Figure 1. PXRD diffractograms of catalysts.
Figure 1. PXRD diffractograms of catalysts.
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Figure 2. STEM-HAADF images and EDX elemental distribution maps of each catalyst.
Figure 2. STEM-HAADF images and EDX elemental distribution maps of each catalyst.
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Figure 3. XPS spectra of Ce 3d (A) and O 1s (B) of catalysts.
Figure 3. XPS spectra of Ce 3d (A) and O 1s (B) of catalysts.
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Figure 4. XPS spectra of Pt 4f of catalysts.
Figure 4. XPS spectra of Pt 4f of catalysts.
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Figure 5. H2-TPR of catalysts.
Figure 5. H2-TPR of catalysts.
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Figure 6. Glycerol conversion and product selectivity of catalysts.
Figure 6. Glycerol conversion and product selectivity of catalysts.
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Figure 7. Pt0/Oads ratio vs. selectivity to GA of catalysts.
Figure 7. Pt0/Oads ratio vs. selectivity to GA of catalysts.
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Table 1. Structural properties of the supports and textural properties of the catalysts.
Table 1. Structural properties of the supports and textural properties of the catalysts.
CatalystAverage Crystallite Size
(nm) a		Lattice Parameter (nm) bSBET
(m2 g−1)		Pore Diameter (nm) cTotal Pore Volume (cm3 g−1) d
Pt/Ce80.5394196110.27
Pt/CeZr60.534438270.14
Pt/CePr50.5410862100.16
Pt/CeTb70.538137480.15
a Scherrer equation; b Bragg equation; c BJH adsorption branch average pore diameter; d quantity of N2 adsorbed at a relative pressure of 0.98.
Table 2. Pt loading, dispersion and average particle size.
Table 2. Pt loading, dispersion and average particle size.
CatalystPt Loading (wt%) aPt Average Particle Size (nm) bPt Average Particle Size (nm) cPt Dispersion (%) b
Pt/Ce0.450.571.6198
Pt/CeZr0.481.669.368
Pt/CePr0.451.368.483
Pt/CeTb0.460.768.5149
a ICP-OES; b H2 chemisorption at −80 °C; c STEM-HAADF particle size distribution.
Table 3. XPS analyses of catalysts.
Table 3. XPS analyses of catalysts.
CatalystAtomic Ratio, XPS
Pt0/(Pt0 + Ptδ+)Oads/(Oads + Olatt)Ce3+/(Ce3+ + Ce4+)M3+/(M3+ + M4+) a
Pt/Ce0.270.180.15---
Pt/CeZr0.210.150.150.00
Pt/CePr0.270.250.060.46
Pt/CeTb0.400.240.070.52
a M corresponds to dopant: Zr; Pr or Tb.
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Rinaudo, M.G.; Yeste, M.d.P.; Vidal, H.; Gatica, J.M.; Cadús, L.E.; Morales, M.R. Insights into Contribution of Active Ceria Supports to Pt-Based Catalysts: Doping Effect (Zr; Pr; Tb) on Catalytic Properties for Glycerol Selective Oxidation. Inorganics 2025, 13, 32. https://doi.org/10.3390/inorganics13020032

AMA Style

Rinaudo MG, Yeste MdP, Vidal H, Gatica JM, Cadús LE, Morales MR. Insights into Contribution of Active Ceria Supports to Pt-Based Catalysts: Doping Effect (Zr; Pr; Tb) on Catalytic Properties for Glycerol Selective Oxidation. Inorganics. 2025; 13(2):32. https://doi.org/10.3390/inorganics13020032

Chicago/Turabian Style

Rinaudo, Matías G., Maria del Pilar Yeste, Hilario Vidal, José M. Gatica, Luis E. Cadús, and Maria R. Morales. 2025. "Insights into Contribution of Active Ceria Supports to Pt-Based Catalysts: Doping Effect (Zr; Pr; Tb) on Catalytic Properties for Glycerol Selective Oxidation" Inorganics 13, no. 2: 32. https://doi.org/10.3390/inorganics13020032

APA Style

Rinaudo, M. G., Yeste, M. d. P., Vidal, H., Gatica, J. M., Cadús, L. E., & Morales, M. R. (2025). Insights into Contribution of Active Ceria Supports to Pt-Based Catalysts: Doping Effect (Zr; Pr; Tb) on Catalytic Properties for Glycerol Selective Oxidation. Inorganics, 13(2), 32. https://doi.org/10.3390/inorganics13020032

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