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Temperature-programmed reduction (TPR) and temperature-programmed desorption (TPD) of methanol and oxygen were used to probe the surface properties, relating to the oxidation reaction of methanol (a representative of oxygenated volatile organic compounds) over a series of monometallic and bimetallic Ru–Au catalysts. The relative amounts of ruthenium and gold in these bimetallic catalysts were found to strongly affect their surface characteristics (TPR and TPD profiles, BET surface areas, surface morphologies observed in SEM micrographs, and XRD patterns) and methanol oxidation activity. Although ruthenium and gold were immiscible in their bulk state, the TPR profiles, SEM micrographs, and XRD patterns provided evidence for the interactions between ruthenium and gold in the bimetallic catalysts, especially the 3.32 wt% Ru–0.61 wt% Au/SiO exhibiting the highest methanol oxidation activity. After the oxidation reaction, even though Ru was oxidized to RuO, the interaction between ruthenium and gold on silica still remained the same. The support material was also found to affect both the catalyst characteristics and the methanol oxidation activity. No bimetallic clusters were observed on the Ru–Au catalysts supported on alumina. Various products, including CO, were found when using the catalysts supported on alumina, causing a higher methanol conversion than the catalysts supported on silica. Graphical Abstract: The objective of the present work was to develop comprehensive information for the interactions of the oxygenated VOC with mono- and bimetallic Ru–Au catalyst surfaces as a function of temperature and gold content. The outcomes of this work directly provide a better understanding of the catalytic oxidation of oxygenated VOCs on the bimetallic Ru–Au catalysts. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Identifying structure-performance relationships is critical for the discovery and optimization of heterogeneous catalysts. Recent theoretical contributions have led to the development of d-band theory, which relates the calculated electronic structure of a metal to its chemical and catalytic activity. While there are many contributions where quantum-chemical calculations have been utilized to validate the d-band theory, experimental examples relating the electronic structures of commercially relevant nonmodel catalysts to their performance are lacking. We show that even small changes in the near-Fermi-level electronic structures of nonmodel supported catalysts, induced by the formation of surface alloys, can be measured and related to the chemical and catalytic performance of these materials. We demonstrate that critical shifts in the d-band center in alloys are related to the formation of new electronic states in response to alloying rather than to charge redistribution among constitutive alloy elements, i.e., the number of d holes and d electrons localized on the constitutive alloy elements is constant. On the basis of the presented results, we provide a simple, physically transparent framework for predicting shifts in the d-band center in response to alloying and relating these shifts to the chemical characteristics of the alloys. [ABSTRACT FROM AUTHOR]

Abstract: We demonstrate that supported Sn/Ni alloy catalyst is more resistant to deactivation via carbon deposition than supported monometallic Ni catalyst in steam reforming of isooctane at moderate steam to carbon ratios, irrespective of the average size of metal particles and the metal loading. The experiments were performed for average diameters of catalytic particles ranging from 30 to 500nm and for the loading of active material ranging from 15 to 44wt% with respect to the total mass of catalyst. The steam reforming reactions were performed at conditions that are consistent with typical solid oxide fuel cell (SOFC) operating conditions. DFT calculations show that the reasons for the enhanced carbon-tolerance of Sn/Ni compared to monometallic Ni are high propensity of Sn/Ni to oxidize carbon and lower driving force to form carbon deposits on low-coordinated metal sites. [Copyright &y& Elsevier]

Abstract: Carbon-induced catalyst deactivation is one of the main problems associated with the electrocatalytic and catalytic reforming of hydrocarbons over supported Ni catalysts. We have used DFT calculations to study various aspects of carbon chemistry on Ni surfaces. We demonstrate that the carbon tolerance of Ni can be improved by synthesizing Ni-containing surface alloys that, compared to monometallic Ni, preferentially oxidize C atoms rather than form C–C bonds and have a lower thermodynamic driving force, associated with the nucleation of carbon atoms on low-coordinated Ni sites. Using the molecular insights obtained in the DFT calculations, we have identified Sn/Ni surface alloy as a potential carbon-tolerant reforming catalyst. The predictions of the DFT calculations were supported by our reactor and catalyst characterization studies, which showed that Sn/Ni is much more resistant to carbon poisoning than monometallic Ni in the steam reforming of methane, propane, and isooctane at moderate steam-to-carbon ratios. [Copyright &y& Elsevier]

[Display omitted] • Pretreating catalysts at 800 °C in air impedes adverse sintering at 1000 °C. • Returning to 800 °C regenerates activity in sintered catalysts by redispersing Pd. • Mechanism for the sintering and redispersion of Pd explored. • Regeneration protocol can be repeatably used, due to persisting trap sites on CeO 2. • Regenerated catalysts effectively co-oxidize CO and C 3 H 8. Methods that can impede or reverse the effects of high-temperature sintering and deactivation are necessary to improve the utilization of catalytic materials. This work demonstrates that exposure to intermediate temperatures (800 °C) can effectively regenerate catalytic performance in sintered Pd-CeO 2 catalysts, through the disintegration and partial redispersion of agglomerated Pd, which increases the abundance of sites that interface strongly with the CeO 2 support. Pretreating the catalyst at 800 °C before sintering forms highly dispersed Pd species that slow the sintering of small, polycrystalline CeO 2 domains. This preserves the density of Ce3+ sites that trap mobile Pd, which improves the efficacy of regeneration. The regenerated catalyst is effective in the co-oxidation of CO and C 3 H 8 , two species which are known to competitively adsorb. The simplicity of this treatment makes it attractive for on-stream regeneration of catalyst performance. [ABSTRACT FROM AUTHOR]

Abstract: The carbon deposition behavior of Ni-based monolith reforming catalysts was studied during n-dodecane autothermal reforming, partial oxidation, and steam reforming. One catalyst formulation was nickel deposited on cerium zirconium oxide (CZO) coated monolith, while the second formulation was nickel directly deposited on bare monolith. In both formulations, a series of catalysts with a range of nickel loadings (0–16wt.%) were prepared to examine the influence of nickel loading on carbon deposition and to elucidate the benefits of the reducible oxide support CZO on carbon deposition. Carbon deposition was generally more pronounced at higher nickel loadings and on catalysts lacking CZO. Nickel supported on bare monolith suffered from excessive carbon deposition and carbon-induced monolith disintegration. The morphologies of carbon were determined by scanning electron microscopy (SEM). Temperature programmed oxidation (TPO) indicated the presence of two types of carbon. The low-temperature TPO peak can be attributed to coating carbon, while the high-temperature peak corresponds to filamentous carbon structures, including large whiskers and smaller filaments. Accumulation of whisker carbon had a deleterious effect on the monolith substrate resulting in the physical destruction of some samples. X-ray diffraction (XRD) gave no evidence for the presence of graphite or carbide species in carbon-deposited catalysts. The experimental results of this study are used to diagnose the causes for nickel catalyst deactivation during autothermal reforming and for proposing strategies to mitigate the deactivation. [Copyright &y& Elsevier]

Abstract: Autothermal reforming (ATR) of n-dodecane was systematically investigated with O/C=0.6 and H2O/C=2.0 over nickel-based catalysts supported on cordierite monoliths. Both nickel supported on monolith (Ni/monolith) and nickel supported on cerium–zirconium oxide (CZO) loaded on monolith (Ni/CZO/monolith) were tested for ATR activity. The influence of nickel weight loading (0–16 wt%) on ATR product yields was examined. Experimental results showed that 2 wt% Ni/CZO/monolith was an optimal composition for ATR. The roles of Ni and CZO were determined by comparing n-dodecane conversion, oxygen conversion, the extent of reforming, and product yields (i.e., CO, CO2, and H2). The reaction studies indicated that nickel catalyzed the conversion of n-dodecane by POX and SR, yielding a hydrogen rich effluent, whereas CZO alone catalyzed the conversion of n-dodecane though catalytic oxidation and cracking, yielding an effluent rich in smaller hydrocarbon species. Nickel supported on CZO showed the greatest hydrogen, carbon monoxide, and carbon dioxide yields of the catalysts studied. ATR, partial oxidation (POX), steam reforming (SR), and the influence of reaction temperature on ATR were studied separately and compared at similar conditions over 2 wt% Ni/monolith and 2 wt% Ni/CZO/monolith to elucidate the primary reforming reactions. An n-dodecane ATR reaction schematic is postulated, and the influences of homogeneous activity and oxygen conversion are discussed. It is proposed that POX, homogeneous cracking, and oxidative cracking are the major routes for n-dodecane conversion during ATR, whereas POX of n-dodecane and SR of smaller hydrocarbons are the primary routes to reforming products (i.e., H2, CO, and CO2). [Copyright &y& Elsevier]

Abstract: The potential of a nickel-ceria-zirconia based catalyst was examined for autothermal reforming of n-dodecane, tetralin and their mixture into a hydrogen-rich product stream suitable for high-temperature fuel cells. n-Dodecane and tetralin were chosen as representative compounds for alkanes and bicyclic compounds in jet fuel. It was possible to reach conversions greater than 90% for both components, as long as sufficiently high oxygen concentrations were maintained in the feed. Tetralin gave larger yields of reforming products than n-dodecane. During the transient start-up phase of the reactor, large temperature excursions were observed, suggesting that the reaction starts with complete combustion of fuel, giving way to autothermal reforming after a few minutes on stream. These high-temperature excursions during reactor start-up are large enough to change the catalyst surface areas. Interestingly, the mixture of tetralin and n-dodecane did not behave as a linear combination of the two pure components, but showed reforming characteristics similar to pure tetralin. The non-linear behavior of the mixture provides a caveat that investigations of single component model compounds may not be able to capture the reforming behavior of more complex fuel mixtures. [Copyright &y& Elsevier]

Abstract: Au, Ag and Au–Ag catalysts on different supports of alumina, titania and ceria were studied for their catalytic activity of ethylene oxidation reactions. An addition of an appropriate amount of Au on Ag/Al2O3 catalyst was found to enhance the catalytic activity of the ethylene epoxidation reaction because Au acts as a diluting agent on the Ag surface creating new single silver sites which favor molecular oxygen adsorption. The Ag catalysts on both titania and ceria supports exhibited very poor catalytic activity toward the epoxidation reaction of ethylene, so pure Au catalysts on these two supports were investigated. The Au/TiO2 catalysts provided the highest selectivity of ethylene oxide with relatively low ethylene conversion whereas, the Au/CeO2 catalysts was shown to favor the total oxidation reaction over the epoxidation reaction at very low temperatures. In comparisons among the studied catalysts, the bimetallic Au–Ag/Al2O3 catalyst is the best candidate for the ethylene epoxidation. The catalytic activity of the gold catalysts was found to depend on the support material and catalyst preparation method which govern the Au particle size and the interaction between the Au particles and the support. [Copyright &y& Elsevier]

Pulse and static hydrogen and oxygen chemisorption techniques for determining the platinum dispersion in bimetallic Pt–Sn catalysts were carried out and compared for a monometallic Pt/Al2O3 catalyst and a series of coimpregnated Pt–Sn catalysts containing 1 wt.% of Pt. The pulse chemisorption method gave lower uptakes of hydrogen and oxygen compared to the static volumetric chemisorption method. The differences in hydrogen and oxygen gas uptake behavior can be attributed to the different equilibration times provided by the two chemisorption methods. In the coimpregnated catalyst series, the O/Pt ratio increased with increasing Sn content. The H/Pt ratio, on the other hand, reached the maximum value at 0.1 wt.% Sn.Pulse chemisorption was then used to evaluate how the preparation method affects platinum dispersion and chemisorption behavior. The alumina-supported catalyst series prepared by coimpregnation of Pt and Sn was compared with a series of catalysts prepared by sequential impregnation with tin first, followed by platinum as second component. Coimpregnation of the Al2O3 support with platinum and small amounts of tin facilitates high Pt dispersion, while sequential impregnation of the support with Sn first, followed by Pt, leads to much lower Pt dispersion. [Copyright &y& Elsevier]

The temperature-programmed desorption (TPD) of methanol, a widely used solvent contributing to industrial VOC emissions, was studied on two different series of Pt–Sn/Al2O3 catalysts that were prepared by coimpregnation and sequential impregnation with Sn first. TPD results showed that methanol decomposed primarily to hydrogen and carbon monoxide. Hydrogen desorbed first, followed by carbon monoxide at higher temperatures. Adding Sn to Pt shifted the desorption peaks of both H2 and CO to higher temperatures. For the coimpregnated Pt–Sn catalysts, the temperature difference between the H2 and CO desorption peak maxima increased systematically with increasing Sn content; for the sequentially impregnated catalysts, the temperature difference remained nearly constant. An exception was the catalyst containing 5 wt.% Sn, where the peaks shifted upward by 150 °C. In both catalyst series, the temperature difference between the hydrogen and the carbon monoxide desorption peak maxima increased with increasing Sn content. This study has demonstrated that the adsorption/desorption behavior of methanol on platinum is strongly modified by the presence of tin.The oxidation of methanol over the monometallic Pt and bimetallic Pt–Sn on alumina support was studied in the temperature range 35–300 °C and initial concentrations of methanol in the range 500–1200 ppm and excess oxygen (21% O2). The experimental results showed that the monometallic Pt catalyst were much more active than the bimetallic catalysts. The coimpregnated catalysts were more active than the sequentially impregnated catalysts. CO2 and methyl formate (CH3OCHO) were the only carbon-containing products of methanol oxidation. Methyl formate was the principle product at low temperatures, while CO2 was the principle product at high temperatures. The reaction order of methanol oxidation was 1.15±0.05. The apparent activation energy of the monometallic platinum catalyst was 14.4 kJ/mol. For the coimpregnated catalysts, addition of tin increased the apparent activation energy while in the sequentially impregnated Pt–Sn the apparent activation energy remained essentially constant over the range 0.6–1.5 wt.% Sn, then shifted to 66.8 kJ/mol for 5 wt.% Sn. [Copyright &y& Elsevier]

Graphical abstract Highlights • OSC is classified into two categories: total and dynamic. • Elemental doping, active component loading, geometrical, and environmental conditions that affect OSC are reviewed. • Measuring techniques and conditions that affect the OSC amount are also discussed. • Typical catalytically reactions related to the role of OSC in automotive emissions control are focused. Abstract CeO 2 is widely used as a catalyst support component due to its redox property of oxygen storage and release. This unique feature, which is usually referred to as "oxygen storage capacity" (OSC), can be quantitatively evaluated by different methods and techniques. Since the oxygen release benefits oxidation reactions, catalytic activity can be correlated with OSC. The measured amount of OSC can be influenced by a number of factors, such as the nature of the reducing agent, the conditions of reducing gas flow and operation temperature, the aging, the composition, and physical and geometric properties of CeO 2 -based materials, and the type of analytical technique used. Therefore, these influencing factors include, but are not limited to, the use of H 2 or CO as reducing agent, continuous or pulsed feed of reducing agent, the presence of other elements in the CeO 2 structure, particle size and surface area, supported catalyst components and aging, etc. This review paper focuses on the measurement of OSC, the effect of influencing factors, and the role of OSC in the typical reactions that occur in automotive emission control like oxidation, NO reduction, water gas shift, and reforming reactions. Furthermore, this review addresses the reactions in which the catalytic activity can be correlated with OSC. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this work was to investigate the catalytic activity of gold catalysts supported on two metal oxides, yttrium oxide and nickel oxide, prepared by co-precipitation for CO and methanol oxidation reactions. The TGA and XRD results confirmed that yttrium hydroxide (Y(OH)3) was formed at calcination temperature below 300°C. When it was calcined at 400°C, the Y(OH)3 was transformed to yttrium oxide hydroxide (YOOH). Finally, when calcination temperature was raised to 600°C, the YOOH was completely transformed to yttrium oxide (Y2O3). Interestingly, the gold loaded on YOOH calcined at 400°C and gold loaded on Y2O3 calcined at 500°C comparatively showed the highest catalytic activity for complete CO oxidation at a reaction temperature of 300°C. The 0.12% Au/Y2O3 catalyst calcined at 500°C was employed for both CO and methanol oxidation studies. For complete CO oxidation, the reaction temperatures of Au/Y2O3 and Au/NiO catalysts were 325°C and 250°C, respectively. The light-off temperatures of Au/Y2O3 and Au/NiO catalysts for methanol oxidation were 210°C and 205°C, respectively. Conclusively, the Au/Y2O3 clearly exhibited the same activity as that of Au/NiO for methanol oxidation while the Au/NiO gave higher activity for CO oxidation. [ABSTRACT FROM AUTHOR]

Abstract: In this study, Ni/Ce0.75Zr0.25O2 catalyst was doped with different amounts of Sn by co-impregnation method. The catalysts were characterized by BET, H2 chemisorption, XRD, TPR, TEM, XPS and tested for iso-octane partial oxidation (iC8POX) to H2 in the temperature range of 400–800°C at atmospheric pressure. The results showed that most of Sn species were present on the surface of Ni particles and did not modify the reducibility of the support. Addition of a small amount of Sn (<0.5wt.%) lowered the catalytic activity for iso-octane partial oxidation by less than 5% while the extent of carbon deposition was decreased by more than 50%. However, Sn loadings higher than 1wt.% caused a massive drop in catalytic activity. This indicates that as long as the Ni surface is only partially covered with Sn species, the active sites for the partial oxidation of iso-octane remain intact, while the surface site ensembles required for carbon formation are blocked. [Copyright &y& Elsevier]

[Display omitted] • A novel method is demonstrated to encapsulate and disperse Ag nanoparticles in a mesoporous TiO 2 nanosphere. • Encapsulation increases Ag-TiO 2 interfacial sites and selectivity, enabling complete oxidation of VOC at lower temperatures. • Post synthesis solvothermal treatment anchors the active metal to the TiO 2 support, providing excellent thermal stability. • Saturating the catalyst's surface with water vapor before beginning the reaction enhances the rate of VOC oxidation. We demonstrate a novel methodology of encapsulating and dispersing Ag nanoparticles in a reducible, mesoporous TiO 2 nanosphere to enhance thermal stability and catalytic activity for VOC oxidation. Through comparisons with surface-impregnated Ag-TiO 2 , which suffer from significant sintering and deactivation after aging at 550 °C, we show that encapsulation helps maintain a uniform Ag particle distribution (2−5 nm) and promotes metal-support interactions by maximizing interfacial sites, thereby improving activity and stability. In addition, we discover that subjecting the encapsulated catalyst to a post-synthesis solvothermal treatment step anchors the active metal more strongly to the support, which helps maintain superior activity under repeated aging cycles. Finally, recognizing that industrial flue gas streams inevitably contain water vapor we examine a constructive method of deliberately exposing the catalyst's surface to water vapor before beginning the reaction. This simple method enhances the rate of VOC oxidation up to six-fold at temperatures as low as 40 °C. [ABSTRACT FROM AUTHOR]

• Pd/SSZ-13 suffers deactivation due to Pd2+ agglomeration to PdO after aging. • Pd tend to move toward outside of zeolite and to agglomerate to large PdO particles. • Dealumination results in Pd2+ ions agglomeration after aging at 900 °C. • The Pd mobility results in deactivation after aging at 800/850 °C. Pd/SSZ-13 samples with the same Pd loading (1 wt.%) but different Si/Al ratio (6 and 13) were hydrothermally aged at 800, 850, and 900 ºC, respectively. The Pd/SSZ-13 with a lower Si/Al ratio suffers a more severe deactivation. The Pd/SSZ-13 with a Si/Al ratio of 6 experiences structural damage due to dealumination, while the structure of the sample with a Si/Al ratio of 13 remains intact. The agglomeration of Pd2+ ions to large PdO particles on the external surface of zeolite causes the deactivation. The Pd cations are mobile during aging. Besides dealumination, the Pd2+ ions might be hydrolyzed and have a high mobility, which also results in the Pd2+ ions agglomeration. The severe dealumination causes the deactivation after aging at 900 ºC. However, the Pd mobility might be the primary reason for the decline of NO adsorption capacity of Pd/SSZ-13 after aging at 800 and 850 °C. [ABSTRACT FROM AUTHOR]

• Co 3 O 4 nanorods and nanoparticles exhibit the same TOF value. • (110) is the main exposed lattice plane for both nanorods and nanoparticles. • Dissociation of surface O 2 * to form surface O* assisted by NO is the rate-determining step. • Surface nitrates and nitrites can be observed by FTIR techniques. Co 3 O 4 nanorods and nanoparticles were prepared and differed in the overall particle sizes and shapes, while in both cases the catalytically active (110) lattice plane was mainly exposed. The forward rate of NO oxidation of Co 3 O 4 nanorods, stated on catalyst weight, was higher than that of Co 3 O 4 nanoparticles. However, the turnover frequency (TOF) numbers normalized by the surface Co3+ were almost the same, indicating that NO oxidation took place over the same active sites of surface Co3+ for both catalysts. Co 3 O 4 nanorods had a larger number of exposed active sites than nanoparticles. The dissociation of surface O 2 *, formed by the quasi-equilibrated reaction of O 2 molecules on vacant sites (*), assisted by gaseous NO to form NO 2 and surface O*, was the rate-determining step in NO oxidation. In situ FTIR spectra confirmed that abundant bridged nitrates were formed on both Co 3 O 4 nanorods and nanoparticles. [ABSTRACT FROM AUTHOR]