Bifunctional Reaction Mechanism Research Articles

Sol-gel auto-combustion synthesis of bimetallic Pt-Co/Al2O3 catalysts for hydrogen production via acetic acid steam reforming

Green hydrogen production from renewable biomass via bio-oil catalytic steam reforming was a prospective technology. In order to accelerate the development of high-performance and long-term catalyst, we selected acetic acid as a typical bio-oil model compound to carry out the studies of steam reforming. Excellent bimetallic Pt-Co/Al2O3 catalysts were prepared using a sol-gel auto-combustion method. The effects of the molar ratio of ethylene glycol: citric acid: metal ions (EG/CA/M) on the catalyst structure and subsequent reforming performance were systematically investigated. It was found that the catalyst’s textural properties, reducibility, basic sites, and the dispersion of active metal could be carefully tuned by the EG/CA/M ratio. The catalyst prepared under EG/CA/M ratio of 6:3:1 performed the best reactivity in acetic acid steam reforming, showing a 97.6% acetic acid conversion and a 96.6% H2 yield at the reaction conditions of 650 °C, steam to carbon molar ratio of 5, and space velocity of 6957 h–1. Furthermore, a bifunctional reaction mechanism of acetic acid catalytic steam reforming was proposed by in-situ diffuse reflective infrared Fourier transform spectroscopy analysis coupled with density functional theory calculations.

Pyrochlore Oxide Decorated with Exsolved Metal Nanoparticles for Enhanced Water Splitting Reaction

Recently, we reported hybrid catalysts consist of metal nanoparticles on a metal oxide support for water splitting reaction, which is synthesized through an in situ exsolution process of metallic nanoparticles on pyrochlore oxide material.1,2 Specifically, we prepared Ni substituted lead ruthenate pyrochlore oxide (Pb2Ru1.6Ni0.4O6.5) via sol-gel crystallization and reduce the samples at different temperatures. Ni nanoparticles supported pyrochlore oxide catalyst significantly accelerate the conversion of Ni to NiOOH due to favorable electron transfer during the oxygen evolution reaction. The hybrid catalyst of pyrochlore oxide with NiRu alloy nanoparticles exhibits superior hydrogen evolution reaction performance, resulting from the bifunctional reaction mechanism, modified electronic structure, and efficient electron transport. Consequently, remarkable water electrolysis performance with superior long-term stability was obtained at the hybrid catalysts.

In Situ Fabrication of Ultrasmall Ni Nanoparticles from Ni(OH)2 Precursors for Efficient CO2 Reforming of Methane

Metal size is a critical structural parameter for Ni-based catalysts in CO2 reforming of methane. Herein, ultrasmall Ni nanoparticles (3.7 nm) were fabricated from Ni(OH)2 precursors on γ-Al2O3 nanoplates via a simple solution method followed by H2 reduction. The resultant Ni/Al2O3-IS catalyst showed competitive reforming performance. The turnover frequency reached 15.3 s–1 at 700 °C under atmospheric pressure. Methane (CH4) conversion declined marginally from 79.8 to 70.2% after 20 h of reaction. Characterization results reveal that high activity and good stability were endowed by the ultrasmall Ni size and superior coke resistance, respectively. A bifunctional reaction mechanism was identified on the Ni/Al2O3-IS catalyst, wherein the activation of the reactant molecules was facilitated near metal–support interfaces. This work offers a novel strategy to fabricate ultrasmall Ni particles and provides new insights into structure–activity relationships in CO2 reforming of methane.

Bifunctional metal-free KAUST Catalysis Center 1 (KCC-1) as highly active catalyst for syngas production via methane partial oxidation

The metal-free KAUST Catalysis Center 1 (KCC-1) was synthesized through microemulsion method with microwave assistance and was assessed for methane partial oxidation (MPO) under various operating conditions. The electronic spin resonance spectroscopy, pyridine-probed infrared spectroscopy, and temperature-programmed desorption of oxygen measurement indicated that the concentration of BrØnsted acid sites and oxygen vacancies in KCC-1 were at least 2-fold higher than its counterparts, which benefited MPO activity via the promotion of adsorption and dissociation of gaseous reactants. The principal species detected by post-reaction X-ray photoelectron spectroscopy (XPS) was surface-adsorbed oxygen species; its relative percentages among all oxygen species reduced in the order spent KCC-1 (77.1%) > spent MCM-41 (Mobil Composition of Matter number 41; 41.4%) > spent SiO2 (−). The catalytic performance followed the same trend, suggesting that the surface-adsorbed oxygen species was the key factor for MPO process. Additionally, the carbon deposition rate increased in the order SiO2 (16.8 mol/gcat/s) > MCM-41 (11.7 mol/gcat/s) > KCC-1 (7.7 mol/gcat/s), consistent with the results of post-reaction Raman measurements. By coupling the in situ Fourier-transform infrared and XPS results, it is suggested that the high concentration of oxygen vacancies in KCC-1 contributed to activate the CH4 molecules on acid sites via different O∗-assisted kinetically relevant C–H bond activation mechanism for combustion-reforming pathway; meanwhile it provided an excellent adsorption-desorption cycle of O2− species to inhibit the carbon deposition, thus creating a bifunctional reaction mechanism in MPO reaction.

Support Induced Effects on the Ir Nanoparticles Activity, Selectivity and Stability Performance under CO2 Reforming of Methane.

The production of syngas (H2 and CO)—a key building block for the manufacture of liquid energy carriers, ammonia and hydrogen—through the dry (CO2−) reforming of methane (DRM) continues to gain attention in heterogeneous catalysis, renewable energy technologies and sustainable economy. Here we report on the effects of the metal oxide support (γ-Al2O3, alumina-ceria-zirconia (ACZ) and ceria-zirconia (CZ)) on the low-temperature (ca. 500–750 °C) DRM activity, selectivity, resistance against carbon deposition and iridium nanoparticles sintering under oxidative thermal aging. A variety of characterization techniques were implemented to provide insight into the factors that determine iridium intrinsic DRM kinetics and stability, including metal-support interactions and physicochemical properties of materials. All Ir/γ-Al2O3, Ir/ACZ and Ir/CZ catalysts have stable DRM performance with time-on-stream, although supports with high oxygen storage capacity (ACZ and CZ) promoted CO2 conversion, yielding CO-enriched syngas. CZ-based supports endow Ir exceptional anti-sintering characteristics. The amount of carbon deposition was small in all catalysts, however decreasing as Ir/γ-Al2O3 > Ir/ACZ > Ir/CZ. The experimental findings are consistent with a bifunctional reaction mechanism involving participation of oxygen vacancies on the support’s surface in CO2 activation and carbon removal, and overall suggest that CZ-supported Ir nanoparticles are promising catalysts for low-temperature dry reforming of methane (LT-DRM).

Bifunctional versus Defect-Mediated Effects in Electrocatalytic Methanol Oxidation.

The most prominent and intensively studied anode catalyst material for direct methanol oxidation fuel cells consists of a combination of platinum (Pt) and ruthenium (Ru). Classically, their high performance is attributed to a bifunctional reaction mechanism where Ru sites provide oxygen species at lower overpotential than Pt. In turn, they oxidize the adsorbed carbonaceous reaction intermediates at lower overpotential; among these, the Pt site‐blocking carbon monoxide. We demonstrate that well‐defined Pt modified Ru(0001) single crystal electrodes, with varying Pt contents and different local PtRu configurations at the surface, are unexpectedly inactive for the methanol oxidation reaction. This observation stands in contradiction with theoretical predictions and the concept of bifunctional catalysis for this reaction. Instead, we suggest that pure Pt defect sites play a more critical role than bifunctional defect sites on the electrodes investigated in this work.

Enhanced Formic Acid Oxidation over SnO2-decorated Pd Nanocubes

The formic acid oxidation reaction (FAOR) is one of the key reactions that can be used at the anode of low-temperature liquid fuel cells. To allow the knowledge-driven development of improved catalysts, it is necessary to deeply understand the fundamental aspects of the FAOR, which can be ideally achieved by investigating highly active model catalysts. Here, we studied SnO2-decorated Pd nanocubes (NCs) exhibiting excellent electrocatalytic performance for formic acid oxidation in acidic medium with a SnO2 promotion that boosts the catalytic activity by a factor of 5.8, compared to pure Pd NCs, exhibiting values of 2.46 A mg–1Pd for SnO2@Pd NCs versus 0.42 A mg–1Pd for the Pd NCs and a 100 mV lower peak potential. By using ex situ, quasi in situ, and operando spectroscopic and microscopic methods (namely, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption fine-structure spectroscopy), we identified that the initially well-defined SnO2-decorated Pd nanocubes maintain their structure and composition throughout FAOR. In situ Fourier-transformed infrared spectroscopy revealed a weaker CO adsorption site in the case of the SnO2-decorated Pd NCs, compared to the monometallic Pd NCs, enabling a bifunctional reaction mechanism. Therein, SnO2 provides oxygen species to the Pd surface at low overpotentials, promoting the oxidation of the poisoning CO intermediate and, thus, improving the catalytic performance of Pd. Our SnOx-decorated Pd nanocubes allowed deeper insight into the mechanism of FAOR and hold promise for possible applications in direct formic acid fuel cells.

Influences of metal-modification and lamellar zeolite structure on ethylene to liquid aromatics conversion reaction using MFI catalysts

The effects of meso-/microporous structure and metal-modification with gallium or zinc on catalytic performances of lamellar MFI zeolites in ethylene conversion reaction to liquid aromatics were investigated. TEM, XRD, Ar adsorption-desorption, UV-Visible spectroscopy, and H2-TPR measurements showed that the zeolite structure is a pivotal factor for controlling the type of metal dopant species forming on zeolite, their size, and their distribution. Adding metal dopants to zeolite structure decreased the Brønsted to Lewis (B/L) acid site ratio in the zeolites and improved their catalytic performance. As a result, metal-modified lamellar MFI zeolites showed higher liquid aromatics yield and selectivity for mono-benzene alkylated aromatics and lower coke formation rate compared to their microporous commercial MFI analogies. Zinc-loaded lamellar MFI had the most efficient catalytic performance among all studied catalysts. This phenomenon can be explained by higher accessibility of reactants to active sites and facilitated transport of products from lamellar structure of this zeolite and the low B/L acid site ratio of this catalyst provided by metal-modification, which is more suitable for ethylene aromatization. A bifunctional reaction mechanism has been proposed based on the analysis results of reaction product distributions that demonstrates the effect of both zeolite acid sites and metal sites in conversion of ethylene to liquid aromatics over MFI zeolite catalysts.

Effect of support oxygen storage capacity on the catalytic performance of Rh nanoparticles for CO2 reforming of methane

The effects of the metal oxide support on the activity, selectivity, resistance to carbon deposition and high temperature oxidative aging on the Rh-catalyzed dry reforming of methane (DRM) were investigated. Three Rh catalysts supported on oxides characterized by very different oxygen storage capacities and labilities (γ-Al2O3, alumina-ceria-zirconia (ACZ) and ceria-zirconia (CZ)) were studied in the temperature interval 400–750 °C under both integral and differential reaction conditions. ACZ and CZ promoted CO2 conversion, yielding CO-enriched synthesis gas. Detailed characterization of these materials, including state of the art XPS measurements obtained via sample transfer between reaction cell and spectrometer chamber, provided clear insight into the factors that determine catalytic performance. The principal Rh species detected by post reaction XPS was Rh0, its relative content decreasing in the order Rh/CZ(100%)>Rh/ACZ(72%)>Rh/γ-Al2O3(55%). The catalytic activity followed the same order, demonstrating unambiguously that Rh0 is indeed the key active site. Moreover, the presence of CZ in the support served to maintain Rh in the metallic state and minimize carbon deposition under reaction conditions. Carbon deposition, low in all cases, increased in the order Rh/CZ < Rh/ACZ < Rh/γ-Al2O3 consistent with a bi-functional reaction mechanism whereby backspillover of labile lattice O2− contributes to carbon oxidation, stabilization of Rh0 and modification of its surface chemistry; the resulting O vacancies in the support providing centers for dissociative adsorption of CO2. The lower apparent activation energy observed with CZ-containing samples suggests that CZ is a promising support component for use in low temperature DRM.

Palladium modified gold nanoparticles as electrocatalysts for ethanol electrooxidation

Resemblin, g core-shell electrocatalysts consisting of a Au core and Pd shell (Au@Pd) are synthesized via a Cu underpotential deposition (UPD)-Pd-displacement method. The Pd shell is non-uniform consisting of tiny Pd clusters with a coverage of 0.5–0.6. The ethanol oxidation reaction (EOR) activity of this kind of structure is much higher than Pd/C in an alkaline solution. The forward peak current density of Au@Pd is 5.4 times higher than that of Pd/C. Furthermore, the onset potential for EOR of the former is ∼100 mV more negative. An interesting particle size dependent EOR activity is also observed. With increasing the Au particle size (2.9, 5.8 and 6.5 nm), the EOR activity increases. The strain and ligand effects from the Au core, together with the bifunctional reaction mechanism in the Au–Pd system may be reasons for the enhanced activity in Au@Pd catalysts.

First-Principles Study of Structure Property Relationships of Monolayer (Hydroxy)Oxide-Metal Bifunctional Electrocatalysts

In the present study, on the basis of detailed density functional theory (DFT) calculations, and using Ni hydroxy(oxide) films on Pt(111) and Au(111) electrodes as model systems, we describe a detailed structural and electrocatalytic analysis of hydrogen evolution (HER) at three-phase boundaries under alkaline electrochemical conditions. We demonstrate that the structure and oxidation state of the films can be systematically tuned by changing the applied electrode potential and/or the nature of substrates. Structural features determined from the theoretical calculations provide a wealth of information that is inaccessible by purely experimental means, and these structures, in turn, strongly suggest that a bifunctional reaction mechanism for alkaline HER will be operative at the interface between the films, the metal substrates, and the surrounding aqueous medium. This bifunctionality produces important changes in the calculated barriers of key elementary reaction steps, including water activation and dissociation, as compared to traditional monofunctional Pt surfaces. The successful identification of the structures of thin metal films and three-phase boundary catalysts is not only an important step towards accurate identification and prediction of a variety of oxide/electrode interfacial structure-properties relationships, but also provides the foundation for rational design and control of ‘targeted active phases’ at catalytic interfaces. The successful design of bifunctional electrocatalysts that exploit these structures, in turn, could ultimately lead to advances in the development of alkaline fuel cells. References 1Surnev, S.; Fortunelli, A.; Netzer, F. P. Chem Rev 2012, 113, 4314. 2Shaikhutdinov, S.; Freund, H.-J. Annu. Rev. Phys. Chem. 2012, 63, 619. 3Subbaraman, R.; Stamenkovic, V.; Markovic, N. et al, Science 2011, 334, 1256. 4Subbaraman, R.; Greeley, J.; Stamenkovic, V.; Markovic, N. et al, Nat Mater 2012, 11, 550 5Strmcnik, D; Stamenkovic, V. R.; Markovic, N. et al, Nat Chem 2013, 5, 300.

Synthesis of nanosized Ce0.85M0.1Ru0.05O2−δ (M = Si, Fe) solid solution exhibiting high CO oxidation and water gas shift activity

Nanosized Ce0.85M0.1Ru0.05O2−δ (M=Si, Fe) has been synthesized using a low temperature sonication method and characterized using XRD, TEM, XPS and H2-TPR. The potential application of both the solid solutions has been explored as exhaust catalysts by performing CO oxidation. The addition of Si- and Fe- in Ce0.95Ru0.05O2−δ greatly enhanced the reducibility of Ce0.85M0.1Ru0.05O2−δ (M=Si, Fe), as indicated by the H2-TPR study. The oxygen storage capacity has been used to correlate surface oxygen reactivity to the CO oxidation activity. Both the compounds reversibly release lattice oxygen and exhibit excellent CO oxidation activity with 99% conversion below 200°C. A bifunctional reaction mechanism involving CO oxidation by the extraction of lattice oxygen and rejuvenation of oxide vacancy with gas feed O2 has been used to correlate experimental data. The performance of both the solid solutions has also been investigated for energy application by performing the water gas shift reaction. The present catalysts are highly active and selective towards the hydrogen production and a lack of methanation activity is an important finding of present study.

Kinetics of carbon monoxide oxidation with Sn0.95M0.05O2−δ(M = Cu, Fe, Mn, Co) catalysts

Base metal substituted Sn0.95M0.05O2−δ (M = Cu, Fe, Mn, Co) catalysts were synthesized by the solution combustion method and characterized by XRD, XPS, TEM and BET surface area analysis. The catalytic activities of these materials were investigated by performing CO oxidation. The rates and the apparent activation energies of the reaction for CO oxidation were determined for each catalyst. All the substituted catalysts showed high rates and lower activation energies for the oxidation of CO as compared to unsubstituted SnO2. The rate was found to be much higher over copper substituted SnO2 as compared to other studied catalysts. 100% CO conversion was obtained below 225 °C over this catalyst. A bifunctional reaction mechanism was developed that accounts for CO adsorption on base metal and support ions and O2 dissociation on the oxide ion vacancy. The kinetic parameters were determined by fitting the model to the experimental data. The high rates of the CO oxidation reactions at low temperatures were rationalized by the high dissociative chemisorption of adsorbed O2 over these catalysts.

Modelling and simulation of a direct ethanol fuel cell considering multistep electrochemical reactions, transport processes and mixed potentials

In this work a one-dimensional mathematical model of a direct ethanol fuel cell (DEFC) is presented. The electrochemical oxidation of ethanol in the catalyst layers is described by several reaction steps leading to surface coverage with adsorbed intermediates (CH 3CO, CO, CH 3 and OH) and to the final products acetaldehyde, acetic acid and CO 2. A bifunctional reaction mechanism is assumed for the activation of water on a binary catalyst favouring the further oxidation of adsorbates blocking active catalyst sites. The chemical reactions are highly coupled with the charge and reactant transport. The model accounts for crossover of the reactants through the membrane leading to the phenomenon of cathode and anode mixed potentials due to the parasitic oxidation and reduction of ethanol and oxygen, respectively. Polarisation curves of a DEFC were recorded for various ethanol feed concentrations and were used as reference data for the simulation. Based on one set of model parameters the characteristic of electronic and protonic potential, the relative surface coverage and the parasitic current densities in the catalyst layers were studied.

Iridium-platinum alloy nanoparticles: Composition-dependent electrocatalytic activity for formic acid oxidation

IrxPt100−x alloy nanoparticles with varied compositions (x = 100, 75, 67, 50, 34, and 0) were synthesized by a thermolytic process at varied ratios of the IrCl3 and PtCl2 precursors. High-resolution transmission electron microscopic (HRTEM) measurements showed that the nanoparticles all exhibited well-defined crystalline structures with the average core diameters around 2 nm; and the elemental compositions were determined by X-ray photoelectron spectroscopic (XPS) measurements. The electrocatalytic activities of the IrxPt100−x nanoparticles toward formic acid oxidation were then examined by electrochemical measurements, including cyclic voltammetry (CV), chronoamperometry, and electrochemical impedance spectroscopy (EIS). In the CV studies, it was found that both the current density of formic acid oxidation and the tolerance to CO poisoning were strongly dependent on the composition of the iridium-platinum alloy nanoparticles, with the best performance found with the Ir50Pt50 nanoparticles. Due to heavy CO poisoning, Pt nanoparticles exhibited the lowest catalytic performance among the series of nanoparticles (excluding Ir nanoparticles). The Ir50Pt50 nanoparticles also showed the maximum current density and stability in chronoamperometric measurements. Consistent results were obtained in electrochemical impedance spectroscopic studies of the electron transfer kinetics involved. Notably, of all the nanoparticle electrocatalysts, an inductive component, i.e. negative impedance, was observed in the potential windows where CO was removed by electro-oxidation; and the charge transfer resistance was found to be the lowest with the Ir50Pt50 nanoparticles. Based on the current density and peak potential of formic acid oxidation, the ratio of the anodic peak current density to the cathodic peak current density measured in CV studies, the stability manifested in chronoamperometric measurements and the tolerance to CO poisoning displayed in EIS measurements, the electrocatalytic performance of the IrPt alloy nanoparticles was found to decrease in the order of Ir50Pt50 > Ir67Pt33 > Ir75Pt25 > Ir34Pt66 > Pt. That is, among the series of IrPt alloy nanoparticles, the sample with the Ir/Pt atomic ratio of 1 : 1 showed the highest electrocatalytic activity towards formic acid oxidation, which might be ascribed to the bifunctional reaction mechanism of bimetallic alloy electrocatalysts.

Low temperature NOx and N2O reduction by H2: Mechanism and development of new nano-catalysts

The understanding of the mechanistic aspects and development of new catalysts for NOx reduction is a priority area of research. Precious metal substituted TiO2 (Ti0.99M0.01O2−δ, where M=Ru, Rh, Pd, Pt) catalysts have been synthesized and investigated for the catalytic reduction of NO by H2. These catalysts have higher activity compared to other catalysts reported in literature. The rate of NO reduction by H2 depends on the reducibility of the catalysts. Temperature programmed reduction experiments with H2 indicate that as the H2 dissociation temperature decreases (reflecting the reducibility of the catalysts), the rate of NO+H2 reaction increases. A new bi-functional reaction mechanism has been developed that accounts for NO adsorption on Mn+ and NO dissociation on the oxide ion vacancy. The kinetic parameters were determined by fitting the model to the experimental data. Consistent with the experimental results, it was found that NO reduction rate was dependent on the adsorption and dissociation of H2 on the metal.

Improved NOx reduction over the staged Ag/Al2O3 catalyst system

Abstract The reaction mechanism of reducing NOx with hydrocarbons over Ag/Al 2 O 3 has been examined to improve its NOx reduction performance at lower temperatures, using ethanol and n -octane as representative hydrocarbon reductants. Based on the results obtained at the early stages of the hydrocarbon oxidation and NO reduction, it is proposed that the partial oxidation of hydrocarbons and the oxidation of NO are the first reaction steps over Ag/Al 2 O 3 . n -Octane is broken up into smaller hydrocarbon molecules, which are then subsequently oxidized to form various aldehydes, while ethanol is also rapidly converted to acetaldehyde. At the same time, NO is oxidized effectively to NO 2 in the presence of reductants. These observations and additional experiments with variable amounts of Al 2 O 3 placed downstream of the Ag/Al 2 O 3 catalyst suggest that the NO reduction by hydrocarbons over Ag/Al 2 O 3 may occur via a bifunctional reaction mechanism; NO and hydrocarbons are converted into NO 2 and more reactive hydrocarbon species (i.e., smaller alkenes, oxygenated hydrocarbons), respectively, over the Ag sites, while N 2 is produced from the subsequent reactions between these intermediate species over different sites including Al 2 O 3 . The proposed bifunctional reaction mechanism offers an opportunity to improve the overall NOx reduction performance of Ag/Al 2 O 3 by optimizing individual reaction steps separately. Thus, the concept of a staged catalyst system has been examined using Ag/Al 2 O 3 for the formation of reaction intermediates, and a secondary catalyst (e.g., Al 2 O 3 or BaY) for the subsequent N 2 production reaction. Significant improvement in NOx reduction to N 2 was obtained at lower temperatures, when BaY was used as the second catalyst and ethanol was used as reductant.

Supported Pt and Pt–Ru catalysts prepared by potentiostatic electrodeposition for methanol electrooxidation

Methanol electrooxidation was investigated on Pt–Ru electrocatalysts supported on glassy carbon. The catalysts were prepared by electrodeposition from solutions containing chloroplatinic acid and ruthenium chloride. Bulk composition analysis of the Pt–Ru catalyst was performed using an X-ray detector for energy dispersive spectroscopy analysis (EDX). Three different compositions were analyzed in the range 0–20 at.% Ru content. Tafel plots for the oxidation of methanol in solutions containing 0.1–2 M CH3OH, and in the temperature range 23–50 °C showed a reasonably well-defined linear region. The slope of the Tafel plots was found to depend on the ruthenium composition. The lower slope was determined for the Pt catalyst, varying between 100 and 120 mV dec−1. The values calculated for the alloys were higher, ranging from 120 to 140 mV dec−1. The reaction order for methanol varies from 0.5 to 0.8, increasing with the ruthenium content. The activation energy calculated from Arrhenius plots was found to change with the catalyst composition, showing a lower value around 30 kJ mol−1 for the alloys, and a higher value, of 58.8 kJ mol−1, for platinum. The effect of ruthenium content is explained by the bifunctional reaction mechanism.

Pd ion substituted CeO2: A superior de-NO catalyst to Pt or Rh metal ion doped ceria

Abstract Pd, Pt and Rh ion doped CeO2, Ce1−xMxO2−δ (M = Pd2+, Pt2+, Rh3+) were synthesized by solution combustion synthesis method and the deNOx activity was investigated by NO + CO reaction. Ionically dispersed Pd in CeO2 was found to have better catalytic activity than ionically dispersed Pt or Rh in CeO2. High rates of NO conversion and high selectivity of N2 is observed over Ce0.98Pd0.02O2−δ. A bi-functional reaction mechanism is proposed, which fits very well with the experimental results. The oxide ion vacancy present in the CeO2 matrix seems to play an important role for product selectivity and high rate of reaction.

NO reduction by H2 over nano-Ce0.98Pd0.02O2−

Abstract Development of new catalysts for controlling nitrogen oxides (NO x ) emissions is an important technical challenge as increasingly strict emission limits are being imposed. A new catalyst Pd 2+ substituted CeO 2 (Ce 0.98 Pd 0.02 O 2− δ ) was synthesized by solution combustion method. The material was characterized by XRD, TEM and XPS and used to investigate the reduction of NO by H 2 . The catalyst shows 100% N 2 selectivity at low temperature and thus is superior to other catalysts reported in literature. A bifunctional reaction mechanism has been proposed to model the experimental data.