Search Results (40)

Platinum was supported on ZSM5 at loadings from 0.1 to 1 wt% and tested for the Selective Catalytic Reduction of NO with H₂ under excess O₂ in a fixed bed reactor to address the issue of NO_x emission abatement from H₂-fueled internal combustion engines avoiding the additional devices for urea storage and injection. To reduce the undesired NO oxidation to NO₂, which is activated by platinum at T > 200 °C, the 0.1%Pt/ZSM5 catalyst was further promoted with sodium. 5 wt% loading of Na strongly inhibited the NO oxidation while giving only a limited impact on the H₂-SCR activity. Unpromoted and Na-promoted catalysts were characterized by XRD, SEM/EDX, N₂ physisorption, and NH₃-TPD to investigate the morphological, structural, and acid properties; H₂ pulse chemisorption and DRIFTS of CO chemisorption were used to investigate the nature of Pt active species. Steady-state and transient operando DRIFTS experiments under NO+H₂+O₂ flow were employed to identify the adsorbed NO_x species interacting with H₂, and reaction intermediates as a function of the reaction conditions. The formation of ammonium intermediates via the reduction of surface nitrate species, playing a key role in H₂-SCR catalyzed by 0.1Pt/ZSM5, was preserved at low Na load whilst NO₂ formation was largely inhibited. Full article

Three MnCeTiO_x catalysts with the same composition were prepared by conventional co-precipitation (MCT-C), reverse co-precipitation (MCT-R), and parallel co-precipitation (MCT-P), respectively, and their low-temperature SCR performance for de-NO_x was evaluated. The textural and structural properties, surface acidity, redox capacity, and reaction mechanism of the catalysts were investigated by a series of characterizations including N₂ adsorption and desorption, XRD, SEM, XPS, H₂-TPR, NH₃-TPD, NO-TPD, and in situ DRIFTs. The results revealed that the most excellent catalytic performance was achieved on MCT-R, and more than 90% NO_x conversion can be obtained at 100–300 °C under a high GHSV of 80,000 mL/(g_cat·H). Furthermore, MCT-R possessed optimal tolerance to H₂O and SO₂ poisoning. The excellent catalytic performance of MCT-R can be attributed to its larger BET specific surface area; higher contents of Mn⁴⁺, Ce³⁺, and adsorbed oxygen species; and more adsorption capacity for NH₃ and NO. Moreover, in situ DRIFTs results indicated that the NH₃-SCR reaction follows simultaneously the Langmuir–Hinshelwood and Eley–Rideal mechanisms at 100 °C. By adjusting the adding mode during the co-precipitation process, excellent low-temperature de-NO_x activity of MCT-R can be obtained simply and conveniently, which is of great practical value for the preparation of a MnCeTiO_x catalyst for denitrification. Full article

Noble metals have become a research hotspot for the oxidation of light alkanes due to their low ignition temperature and easy activation of C-H; however, sintering and a high price limit their industrial applications. The preparation of effective and low-noble-metal catalysts still presents profound challenges. Herein, we describe how a Ru@CoMn₂O₄ spinel catalyst was synthesized via Ru in situ doping to promote the activity of propane oxidation. Ru@CoMn₂O₄ exhibited much higher catalytic activity than CoMn₂O₄, achieving 90% propane conversion at 217 °C. H₂-TPR, O₂-TPD, and XPS were used to evaluate the catalyst adsorption/lattice oxygen activity and the adsorption and catalytic oxidation capacity of propane. It could be concluded that Ru promoted synergistic interactions between cobalt and manganese, leading to electron transfer from the highly electronegative Ru to Co²⁺ and Mn³⁺. Compared with CoMn₂O₄, 0.1% Ru@CoMn₂O₄, with a higher quantity of lattice oxygen and oxygen mobility, possessed a stronger capability of reducibility, which was the main reason for the significant increase in the activity of Ru@CoMn₂O₄. In addition, intermediates of the reaction between adsorbed propane and lattice oxygen on the catalyst were monitored by in situ DRIFTS. This work highlights a new strategy for the design of a low-noble-metal catalyst for the efficient oxidation of propane. Full article

Catalytic oxidation is widely recognized as a highly effective approach for eliminating highly toxic CO. The current challenge lies in designing catalysts that possess exceptional low-temperature activity and stability. In this work, we have prepared ultrafine platinum particles of ~1 nm diameter dispersed on a MgFe₂O₄ support and found that the addition of 3 wt.% FeO_x into the 3Pt/MgFe₂O₄ significantly improves its activity and stability. At an ultra-low temperature of 30 °C, the CO can be totally converted to CO₂ over 3FeO_x-3Pt/MgFe₂O₄. High and stable performances of CO-catalytic oxidation can be obtained at 60 °C on 3FeO_x-3Pt/MgFe₂O₄ over 35 min on-stream at WHSV = 30,000 mL/(g·h). Based on a series of characterizations including BET, XRD, ICP, STEM, H₂-TPR, XPS, CO-DRIFT, O₂-TPD and CO-TPD, it was disclosed that the relatively high activity and stability of 3FeO_x-3Pt/MgFe₂O₄ is due to the fact that the addition of FeO_x could facilitate the antioxidant capacity of Pt and oxygen mobility and increase the proportion of adsorbed oxygen species and the amounts of adsorbed CO. These results are helpful in designing Pt-based catalysts exhibiting higher activity and stability at low temperatures for the catalytic oxidation of CO. Full article

A series of Co₃O₄ catalysts were synthesized and derived from Co-BTC (BTC = 1,3,5-benzenetricarboxylic acid). The effects of different calcination temperatures and calcination atmospheres on the catalytic activity of the materials were investigated. The characteristics of the catalysts were investigated by using various techniques, including X-ray diffraction, N₂ adsorption–desorption measurements, scanning electron microscopy, X-ray photoelectron spectroscopy, and H₂ temperature-programmed reduction. The findings demonstrated that an increase in calcination temperature caused a higher agglomeration of grains, reduced the specific surface area, and influenced the contents of the active substance Co³⁺ and surface-adsorbed oxygen of the catalyst. The catalyst pretreated under the N₂ atmosphere showed a more uniform particle distribution, better low-temperature reducibility, and the highest catalytic activity. The in situ DRIFTS results indicated that toluene was decomposed successively to benzaldehyde, benzoic acid, bicarbonate, and carbonate species and was eventually broken down into small molecules of CO₂ and H₂O as the temperature increased. Full article

Catalytic conversion of ethanol to 1-butanol was studied over MgO–Al₂O₃ mixed oxide-based catalysts. Relationships between acid-base and catalytic properties and the effect of active metal on the hydrogen transfer reaction steps were investigated. The acid-base properties were studied by temperature-programmed desorption of CO₂ and NH₃ and by the FT-IR spectroscopic examination of adsorbed pyridine. Dispersion of the metal promoter (Pd, Pt, Ru, Ni) was determined by CO pulse chemisorption. The ethanol coupling reaction was studied using a flow-through microreactor system, He or H₂ carrier gas, WHSV = 1 ${\mathrm{g}}_{\mathrm{E}\mathrm{t}\mathrm{O}\mathrm{H}}·{\mathrm{g}}_{\mathrm{c}\mathrm{a}\mathrm{t}.}^{-1}·{\mathrm{h}}^{-1}$, at 21 bar, and 200–350 °C. Formation and transformation of surface species under catalytic conditions were studied by DRIFT spectroscopy. The highest butanol selectivity and yield was observed when the MgO–Al₂O₃ catalyst contained a relatively high amount of strong-base and medium-strong Lewis acid sites. The presence of metal improved the activity both in He and H₂; however, the butanol selectivity significantly decreased at temperatures ≥ 300 °C due to acceleration of undesired side reactions. DRIFT spectroscopic results showed that the active metal promoted H-transfer from H₂ over the narrow temperature range of 200–250 °C, where the equilibrium allowed significant concentrations of both dehydrogenated and hydrogenated products. Full article

Cu-doped manganese oxide (Cu–Mn₂O₄) prepared using aerosol decomposition was used as a CO oxidation catalyst. Cu was successfully doped into Mn₂O₄ due to their nitrate precursors having closed thermal decomposition properties, which ensured the atomic ratio of Cu/(Cu + Mn) in Cu–Mn₂O₄ close to that in their nitrate precursors. The 0.5Cu–Mn₂O₄ catalyst of 0.48 Cu/(Cu + Mn) atomic ratio had the best CO oxidation performance, with T₅₀ and T₉₀ as low as 48 and 69 °C, respectively. The 0.5Cu–Mn₂O₄ catalyst also had (1) a hollow sphere morphology, where the sphere wall was composed of a large number of nanospheres (about 10 nm), (2) the largest specific surface area and defects on the interfacing of the nanospheres, and (3) the highest Mn³⁺, Cu⁺, and Oads ratios, which facilitated oxygen vacancy formation, CO adsorption, and CO oxidation, respectively, yielding a synergetic effect on CO oxidation. DRIFTS-MS analysis results showed that terminal-type oxygen (M=O) and bridge-type oxygen (M-O-M) on 0.5Cu–Mn₂O₄ were reactive at a low temperature, resulting in-good low-temperature CO oxidation performance. Water could adsorb on 0.5Cu–Mn₂O₄ and inhibited M=O and M-O-M reaction with CO. Water could not inhibit O₂ decomposition to M=O and M-O-M. The 0.5Cu–Mn₂O₄ catalyst had excellent water resistance at 150 °C, at which the influence of water (up to 5%) on CO oxidation could be completely eliminated. Full article

The adsorption and photocatalytic degradation of trimethyl phosphate (TMP) and triethyl phosphate (TEP), two environmentally relevant model pollutants, have been studied on commercial anatase TiO₂ and sulfate-terminated anatase TiO₂ nanoparticles by means of operando diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and 2D correlation spectroscopy (2D COS). It is concluded that both TMP and TEP adsorb dissociatively on anatase TiO₂, while on the sulfate-terminated anatase TiO₂, TMP and TEP adsorb associatively. Upon UV illumination, TMP and TEP are completely oxidized on sulfate-terminated anatase TiO₂, as evidenced by the evolution of the IR bands characteristic for water and carbon dioxide. In contrast, on anatase TiO₂, UV illumination leads to the formation of stable surface-coordinated carboxylate products, which impedes complete oxidation. 2D COS analysis suggests that parallel reaction pathways occur during oxidation under UV illumination, viz. methoxide/ethoxide (ads) → carboxylates (ads) and methoxide/ethoxide (ads) → aldehydes (ads) → carboxylates (ads). A parallel reaction occurs on sulfated TiO₂ that yields CO₂ and H₂O by direct radical reactions with the methoxide groups with little, or no, formation of surface-coordinated intermediates. Sulfated TiO₂ favor the formation of aldehyde intermediates, with reaction rates 10 times and 30 times faster for TMP and TEM, respectively, compared with commercial anatase TiO₂. About 37% (33%) and 32% (24%) of TMP (TEP) were degraded on sulfated-terminated TiO₂ and pure TiO₂, respectively, after the first 9 min of UV illumination. We show that the sulfate-functionalization of TiO₂ has two main functions. First, it prevents the formation of strongly bonded bridging carboxylates, thereby alleviating deactivation. Second, it promotes full oxidation of the organic side-chains into carbon dioxide and water. Improved electron-hole separation by the electrophilic S(VI) in combination with the blocking of bridging reaction intermediates is proposed to contribute to the improved activity. The presented results give insights into how acidic surface modifications change adsorbate surface chemistries, which can be used to increase the sustained activity of low-temperature photocatalysts. Full article

We combine operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) with on-line mass spectrometry (MS) to study the correlation between the oxidation state of titania-supported IrO₂ catalysts (IrO₂@TiO₂) and their catalytic activity in the prototypical CO oxidation reaction. Here, the stretching vibration of adsorbed CO_ad serves as the probe. DRIFTS provides information on both surface and gas phase species. Partially reduced IrO₂ is shown to be significantly more active than its fully oxidized counterpart, with onset and full conversion temperatures being about 50 °C lower for reduced IrO₂. By operando DRIFTS, this increase in activity is traced to a partially reduced state of the catalysts, as evidenced by a broad IR band of adsorbed CO reaching from 2080 to 1800 cm⁻¹. Full article

A comprehensive study of the catalytic properties of the copper-iron binary system supported on mordenite, depending on the iron valence—CuFe2MOR and CuFe3MOR—was carried out, and redox ability has been considered as a decisive factor in determining catalytic efficiency. Acidity was studied by TPD-NH₃, DRIFT-OH, and DRT methods. The total acidity of both samples was high. The Brönsted acidity is similar for both bimetallic samples and is explained by the acidity of zeolite; Lewis acidity varies greatly and depends on the exchange cations. A screening DRIFT study of CO and NO has shown redox capacity and demonstrated a potential for using these materials as catalysts for ambient protection. CuFe2MOR demonstrated stable Cu and Fe species, while CuFe3MOR showed redox dynamic species. As expected, CuFe3MOR displayed higher catalytic performance in NO reduction via CO oxidation, because of the easily reduced intermediate NO-complex adsorbed on the metallic Cu and Fe sites, which were observed through in situ DRIFT study. Full article

CO₂ emissions in the atmosphere have been increasing rapidly in recent years, causing global warming. CO₂ methanation reaction is deemed to be a way to combat these emissions by converting CO₂ into synthetic natural gas, i.e., CH₄. NiRu/CeAl and NiRu/CeZr both demonstrated favourable activity for CO₂ methanation, with NiRu/CeAl approaching equilibrium conversion at 350 °C with 100% CH₄ selectivity. Its stability under high space velocity (400 L·g⁻¹·h⁻¹) was also commendable. By adding an adsorbent, potassium, the CO₂ adsorption capability of NiRu/CeAl was boosted, allowing it to function as a dual-function material (DFM) for integrated CO₂ capture and utilisation, producing 0.264 mol of CH₄/kg of sample from captured CO₂. Furthermore, time-resolved operando DRIFTS-MS measurements were performed to gain insights into the process mechanism. The obtained results demonstrate that CO₂ was captured on basic sites and was also dissociated on metallic sites in such a way that during the reduction step, methane was produced by two different pathways. This study reveals that by adding an adsorbent to the formulation of an effective NiRu methanation catalyst, advanced dual-function materials can be designed. Full article

The conversion of ethanol towards ethylene and diethyl ether in the presence of catalysts requires special consideration from the perspective of green chemistry. Ethanol dehydration was studied on a complex titanium phosphate MAlTiP (M_0.5(1+x)Al_xTi_2-x(PO₄)₃ with M = Ni, Mn (x = 0; 0.2)) catalysts, alongside a NASICON-type structure synthesized by the sol–gel method. The initial catalysts were characterized by N₂ gas sorption, SEM, XRD and spectroscopic methods (Raman and DRIFT of adsorbed CO and C₆H₆). The results revealed that all catalysts exhibited high activity and selectivity at 300–420 °C. The conversion of ethanol increases with the reaction temperature, reaching 67–80% at 420 °C. The MnAlTiP exhibited the highest ethylene selectivity among other catalysts, with 87% at 420 °C. The aluminum modification improved the acid properties of the catalysts, due to the appearance of Lewis acid sites (LAS) and the strength moderate Brønsted acid sites (BAS). It was shown that the activity of complex phosphates in ethanol dehydration increases with the strength of the Brønsted acid sites (BAS). Full article

It is still an intractable problem to exploit high-efficient Co-based catalysts for low-temperature HCHO oxidation. Herein, we synthesized a series of Cu-doped Co₃O₄ catalysts (Cu₁Co₈, Cu₁Co₄, and Cu₁Co₂ corresponded to 1/8, 1/4, and 1/2 of Cu/Co molar ratios, respectively) via in situ pyrolysis of bimetal Cu-ZIF-67 precursors and the pure Co₃O₄ sample was also prepared through directly annealing monometal ZIF-67 for comparison. Performance tests of HCHO oxidation found that Cu doping remarkably enhanced the low-temperature HCHO oxidation performance of Co₃O₄ sample, and thereinto the Cu₁Co₄ possessed the optimal HCHO oxidation activity, which achieved 90% HCHO conversion at 108 °C. The characterization results revealed that the stronger interaction between Cu and Co species (Co²⁺ + Cu²⁺ ↔ Co³⁺ + Cu⁺) of Cu₁Co₄ not only facilitates the formation of defect sites, Co³⁺ and surface adsorbed oxygen species but also improves its low-temperature reducibility, and consequently resulting in its superior HCHO oxidation performance. Furthermore, the in-situ DRIFTS results suggested that the formaldehyde oxidation over Cu₁Co₄ followed HCHO → H₂CO₂ → HCOO⁻ → CO₃²⁻ → CO₂ pathway. The present work provides a novel and facile approach to fabricating highly effective Co-based catalysts for low-temperature HCHO oxidation. Full article

One of the current problems in the environmental catalysis is the design of an effective and less costly catalytic system for the oxidation of CO. The nano-sized α-Mn₂O₃ oxide has been prepared and modified with 0.5 wt.% Pt. The catalysts have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), temperature-programmed reduction (TPR) and diffuse-reflectance infrared spectroscopy (DRIFTS). Finely divided PtO and Pt(OH)₂ are being formed on the Mn₂O₃ surface as a result of the strong interaction between platinum and the nano-oxide. Based on DRIFTS investigations and the model calculations, a Langmuir–Hinshelwood type of mechanism is supposed for CO oxidation on Pt/Mn₂O₃. The CO and oxygen are adsorbed on different types of sites. The Mars–van Krevelen mechanism is the most probable one over pure Mn₂O₃, thus suggesting that CO₂ is adsorbed on the oxidized sites. The CO adsorption in the mixture CO + N₂ or in the presence of oxygen (CO + N₂ + O₂) leads to a partial reduction in the Pt⁺ surface species and the formation of linear Pt¹⁺−CO and Pt⁰−CO carbonyls. Both of them take part in the CO oxidation reaction. Full article

In this work, the impact of TiO₂ properties on the CO₂ adsorption properties of titanium dioxide modified with 3-aminopropyltriethoxysilane (APTES) was presented. The APTES-modified TiO₂ materials were obtained by solvothermal process and thermal modification in the argon atmosphere. The prepared adsorbents were characterized by various techniques such as X-ray diffraction (XRD), Fourier transform infrared (DRIFT), thermogravimetric analysis and BET specific surface area measurement. CO₂adsorption properties were measured at different temperatures (0, 30, 40, 50 and 60 °C). Additionally, the carbon dioxide cyclic adsorption-desorption measurements were also investigated. The results revealed that modifying TiO₂ with APTES is an efficient method of preparing CO₂ sorbents. It was found that the CO₂ adsorption capacity for the samples after modification with APTES was higher than the sorption capacity for unmodified sorbents. The highest sorption capacity reached TiO₂-4 h-120 °C-100 mM-500 °C sample. It was also found that the CO₂ adsorption capacity shows excellent cyclic stability and regenerability after 21 adsorption-desorption cycles. Full article