Eley-Rideal Mechanism Research Articles

Strikingly Facile Cleavage of N-H/N-O Bonds Induced by Surface Frustrated Lewis Pair on CeO2(110) to Boost NO Reduction by NH3.

Ceria with surface solid frustrated Lewis pairs (FLPs), formed by regulating oxygen vacancies, demonstrate remarkable ability in activating small molecules. In this work, we extended the application of FLPs on CeO2(110) to the selective catalytic reduction of NO by NH3 (NH3-SCR), finding a notable enhancement in performance compared to ordinary CeO2(110). Additionally, an innovative approach involving H2 treatment was discovered to increase the number of FLPs, thereby further boosting the NH3-SCR efficiency. Typically, NH3-SCR on regular CeO2 follows the Eley-Rideal (E-R) mechanism. However, density functional theory (DFT) calculations revealed a significant reduction in the energy barriers for the activation of N-O and N-H bonds under the Langmuir-Hinshelwood (L-H) mechanism with FLPs present. This transition shifted the reaction mechanism from the E-R pathway on regular R-CeO2 to the L-H pathway on FLP-rich FR-CeO2, as corroborated by the experimental findings. The practical application of FLPs was realized by loading MoO3 onto FLP-rich FR-CeO2, leveraging the synergistic effects of acidic sites and FLPs. This study provides profound insights into how FLPs facilitate N-H/N-O bond activation in small molecules, such as NH3 and NO, offering a new paradigm for catalyst design based on catalytic mechanism research.

Atomic Level Understanding of the Structural Stability and Catalytic Activity of Nanoporous Gold/Titania Cluster Inverse Catalysts at Ambient and High Temperatures.

Nanoporous gold (NPG) exhibits exceptional catalytic performance at low temperatures, but its activity declines at elevated temperatures due to structural coarsening. Loading metal oxide nanoparticles onto NPG can enhance its catalytic activity at high temperatures. In this work, we used NPG-supported titania nanoparticles as a model system (denoted as Ti2O4/NPG) to study their catalytic activity at ambient and high temperatures with CO oxidation as a probe reaction by density functional theory (DFT) calculation and ab initio molecular dynamics (AIMD) simulations. The possible factors that may affect the CO oxidation reaction pathways and energy profiles on the Ti2O4/NPG, such as oxygen vacancies; silver impurities; Mars-van Krevelen (MvK), Eley-Rideal (ER), or trimolecular Eley-Rideal (TER) mechanisms; and catalytic active sites, were comprehensively investigated. The results showed that reaction energy barriers on Ti2O4/NPG were not significantly decreased compared to the pristine NPG, indicating that their catalytic activities at ambient temperature were comparable. At the evaluated temperature (400 °C), the Ti2O4/NPG exhibited superior thermal stability and maintained its active sites, while the NPG reduced active sites due to surface coarsening. The strong oxide-metal interaction (SOMI) effect between the NPG and Ti2O4 nanoparticles is found to be a main factor for the high structural stability and catalytic activity at high temperatures.

Embedding Reverse Electron Transfer Between Stably Bare Cu Nanoparticles and Cation-Vacancy CuWO4.

Cu nanoparticles (NPs) have attracted widespread attention in electronics, energy, and catalysis. However, conventionally synthesized Cu NPs face some challenges such as surface passivation and agglomeration in applications, which impairs their functionalities in the physicochemical properties. Here, the issues above by engineering an embedded interface of stably bare Cu NPs on the cation-vacancy CuWO4 support is addressed, which induces the strong metal-support interactions and reverse electron transfer. Various atomic-scale analyses directly demonstrate the unique electronic structure of the embedded Cu NPs with negative charge and anion oxygen protective layer, which mitigates the typical degradation pathways such as oxidation in ambient air, high-temperature agglomeration, and CO poisoning adsorption. Kinetics and in situ spectroscopic studies unveil that the embedded electron-enriched Cu NPs follow the typical Eley-Rideal mechanism in CO oxidation, contrasting the Langmuir-Hinshelwood mechanism on the traditional Cu NPs. This mechanistic shift is driven by the Coulombic repulsion in anion oxygen layer, enabling its direct reaction with gaseous CO to form the easily desorbed monodentate carbonate.

Improved surface acidity of CeO2/TiO2 catalyst by Cu doping to enhance the SCR catalytic activity

The catalyst is based on CeO2 cannot be widely used in SCR reaction because of its poor NH3 adsorption performance. In this study, Cu-doped CeTi catalyst was designed. The results show that the CeTiCu0.3 has a wide active temperature window of 200–450 °C in NH3-SCR reaction, and NO conversion is > 80%. This is mainly due to the fact that Cu doping provides more acidic sites on the surface of CeTi catalyst, especially the increase of Lewis acid sites is more obvious. NH3-TPD showed that CeTiCu0.3 had a large NH3 adsorption capacity and was mainly adsorbed at Lewis acid sites. In situ DRIFTs results show that NH3 first adsorbs on the Lewis acid site of catalyst in coordination state and reacts with gaseous NOx, while NOx adsorbed on catalyst surface has low reactivity. Therefore, the CeTiCu0.3 catalyst is mainly controlled by the Eley–Rideal mechanism. More Lewis acid sites, and abunda nt Cu2+/Cu+ and Ce4+/Ce3+ formed Cu2+, Ce3+ and surface reactive oxygen species are the main reasons for the excellent catalytic performance of CeTiCu.

Novel framework-confined Cu@ 13X catalyst with excellent resistance to toxic SO2 as an eco-friendly substitute for hazardous V-based NH3-SCR catalyst

V2O5-WO3/TiO2 (VWTi) catalyst has long been utilized in fixed source flue gases to purify harmful NO gas. However, VWTi is classified as a hazardous material because of its harm to human health and environment. To address this issue, a low-cost green Cu-based zeolite catalyst (Cu@13X) with a wide temperature range was synthesized using an in-situ hydrothermal method. This method is intended to control the adsorption capacity of toxic SO2 by regulating the location of Cu species. UV-Vis DRS and EXAFS analyses revealed that a significant amount of Cu was encapsulated within the 12-membered ring pores of the 13X molecular sieve. SO2-TPD and DFT calculations further indicated that Cu@ 13X exhibits reduced SO2 chemical adsorption capacity. Consequently, this green catalyst demonstrated superior catalytic performance, maintaining superior NOx conversion for over 70 h in the mixture gas containing 250 ppm SO2; while the Cu/13X catalyst lacked NH3-SCR catalytic activity under the same conditions. Moreover, Cu@ 13X catalyst also has excellent NH3-SCR catalytic performance in low temperature flue gas below 250 °C, which is significantly better than the hazardous VWTi catalyst. Characterization techniques such as NH3-TPD, H2-TPR, and XPS confirmed that the Cu@ 13X catalyst possesses excellent acidity, robust redox capabilities, and abundant surface defects. In-situ DRIFT spectra further illustrated that the NH3-SCR reaction on the catalyst surface adheres to the Eley-Rideal mechanism both before and after the introduction of toxic SO2. This study offers a fresh perspective on the development of framework-confined NH3-SCR catalysts and elucidates the mechanism behind the sulfur resistance of these catalysts. And the green Cu@ 13X catalyst is anticipated to serve as an effective alternative to the hazardous VWTi catalyst.

Temperature-induced evolution of CuOx clusters in CuOx/TiO2 catalyst for boosting auto-exhaust oxidation

Developing non-noble metal oxides, replacing platinum group catalysts for auto-exhaust purification, where their usage amount exceeds 40 % of global demand, remains a challenge. Herein, we presented a combined approach on the synthesis and application of robust CuOx/TiO2 catalysts with ultra-fine CuOx clusters (ca. 1 nm). The strong interaction between CuOx and TiOx induces favorable interfacial charge accumulation, facilitating the extraction of the interfacial oxygen atoms in Cu2-x-O-Ti4-y chains and the surface lattice oxygen on CuOx clusters. Isotope 18O2 experiments and DFT calculations jointly confirmed that these oxygen atoms preferentially participate in the oxidation through the Mars-van Krevelen mechanism below 250 °C. The resulted oxygen vacancies facilitate the adsorption and activation of O2 molecules, which will participate the oxidation above 250 °C through Eley-Rideal mechanism. The increase in the temperature also drives the synergy of active oxygen species in the interfacial Cu2-x-O-Ti4-y bond chains and on CuOx clusters, cooperatively promoting the conversion of NO to NO2. As a result, the CuOx/TiO2 catalyst exhibits exceptional catalytic performance in soot oxidation, with a four-fold higher reaction rate (4.17 μmol g−1 min−1) than that of single-atom Cu₁-TiO2 catalyst. Such findings provide a novel strategy for the advancement of Cu-based cluster catalysts in environmental applications.

Insights into the mechanism of enhancing resistance of MnAlOx-Str NH3-SCR catalyst derived from streptomycin waste residue and LDHs

Streptomycin waste residue composited with Layered double hydroxides (LDHs) derived Mn1Al1Ox-Str-2 catalyst was proposed for NH3 selective catalytic reduction (NH3-SCR) denitration technology, which improved the overall catalytic performance. In the wide temperature range of 150-300℃, the preferred Mn1Al1Ox-Str-2 catalyst had Nitrogen oxides (NOx) conversion of exceeded 96%, which was higher than that of the control Mn1Al1Ox and Mn/Al2O3 catalysts. In addition, Mn1Al1Ox-Str-2 catalyst had better resistance to SO2 and/or H2O, as well as good regeneration ability. Various analytical techniques had confirmed that the Mn1Al1Ox-Str-2 catalyst derived from streptomycin residue composite LDHs precursor had better surface properties with more active species, abundant surface oxygen, higher reduction capacity and better adsorption of NOx and NH3. Analytical techniques revealed that the Lewis acid site on the surface of Mn1Al1Ox-Str-2 catalyst was involved in SCR reaction and both the Eley-Rideal mechanism and Langmuir-Hinshelwood mechanism existed simultaneously in the NH3-SCR reaction, and SO2 had a weak effect on the adsorption of reactants with fewer sulfate species formation. This work provided feasible strategies for efficient and stable SCR technology and efficient utilization of streptomycin residue waste resources, which was significant for the design and application of SCR technology in the future.

CO oxidation on single Pt atom supported by two-dimensional ZnO monolayer: Reaction mechanism and precursor activation

CO oxidation is an effective solution for controlling CO emissions, and supported single-atom catalysts have shown excellent catalytic reactivity for chemical reactions. CO oxidation on a single Pt atom supported by a two-dimensional ZnO monolayer is investigated by combing ab initio molecular dynamics and density functional theory calculations. Seven reaction mechanisms are identified, including two new trimolecular Elie-Riedel mechanisms; six of them, except for the Mars-van Krevelen mechanism, have rate-limiting step energy barriers between 0.31 and 0.47 eV, which is lower than the experimental activation barrier of 0.81 eV on single Pt atoms supported by bulk ZnO, and is much lower than that of about 1.0 eV on Pt(111) surface. Furthermore, two preferred reaction mechanisms are discovered, an Eley-Rideal mechanism and a trimolecular Eley-Rideal mechanism, both of which have rate-limiting step energy barriers as low as 0.31 eV. Our results show that the more antibonding orbitals are filled in the reaction precursor, the higher its activation level. Activation of precursors plays an important role in CO oxidation and leads to different mechanisms. These results provide insights into the design of efficient single-atom catalysts supported by two-dimensional materials for the removal of CO pollutants.

Highly efficient Fe-Cu/CL catalysts based on low-cost clay minerals for NH3-SCR of NOx at low temperature

One of the main challenges for NH3-SCR of NOx at low temperatures is developing a catalyst with exceptional low-temperature catalytic activity. Herein, four kinds of clay minerals including halloysite (Hte), Ca-montmorillonite (Ca-Mte), chlorite (Cte), and Na-montmorillonite (Na-Mte) were used as supports and impregnated with Fe and Cu to synthesize Fe-Cu/Hte, Fe-Cu/Ca-Mte, Fe-Cu/Cte, and Fe-Cu/Na-Mte catalysts, respectively. Within a temperature range of 180–240 °C, the resultant Fe-Cu/Hte catalyst produced more than 98 % NOx conversion and demonstrated the best low-temperature NH3-SCR catalytic performance. The characterization results indicated that the weakened crystallinity of active species, high ratios of Fe3+/Fe and Cu+/Cu, and more surface absorbed oxygen species, as well as excellent low-temperature redox ability and surface acidity all contributed to its outstanding low-temperature catalytic activity. The in situ DRIFT study at 240 ℃ showed that two forms of the Eley-Rideal (E-R) mechanism existed on the Fe-Cu/Hte and Fe-Cu/Cte catalysts, while the E-R and Langmuir-Hinshelwood (L-H) processes were both involved over the Fe-Cu/Ca-Mte and Fe-Cu/Na-Mte catalysts.

Probing the role of nanoconfinement in improving N2 selectivity of Mn-based catalysts during NH3-SCR

Mn-based catalysts are promising low-temperature NH3-SCR catalysts, yet their strong oxidative capability leads to excessive N2O production, contributing to global warming. This study explored titanium nanotubes supported MnOx catalysts for NH3-SCR. The optimal catalyst, 10%Mn/TN showed remarkable NOx conversion over 95 % at 150–400 °C, together with a N2 selectivity surpassing 95 % below 300 °C. In contrast, 10%Mn/Ti catalyst used for comparison had a N2 selectivity as low as 30 %. The active Mn species may predominantly locate within the inner regions of the titanium nanotubes, which effectively regulated the redox properties of 10%Mn/TN. Density Functional Theory (DFT) calculations showed that the decomposition of NH4NO3 formed on 10%Mn/TN into H2O and N2O was more difficult than that on 10%Mn/Ti. Furthermore, the NH3-SCR reaction on 10%Mn/TN mainly followed the Eley-Rideal mechanism and NH4NO3 decomposition was effectively inhibited, consequently leading to a significant improvement in N2 selectivity. These findings offer crucial insights for the design and development of Mn-based catalysts with superior activity and N2 selectivity in NH3-SCR applications.

Mechanism insight into esterification of levulinic acid with methanol on H-Beta Zeolite: A DFT study

The esterification of levulinic acid (LA) to alkyl levulinate esters from biomass by heterogeneous acid catalysis is a potential chemical route for the sustainable production of high value-added products. Acidic zeolites are promising catalysts for this conversion due to their unique pore structures, high selectivity and strong acidity. In this work, we use Density Functional Calculations (DFT) to study the reaction mechanisms for the esterification of LA with MeOH on H-Beta zeolite. We have studied two mechanisms that we consider relevant to the formation of methyl levulinate in acidic zeolites, one involving an Eley-Rideal type mechanism and the other a Langmuir-Hinshelwood type mechanism. Since the activation energies of the rate-determining steps are quite similar, our results suggest that both mechanisms are favourable for this reaction, depending on how the LA and MeOH molecules are initially adsorbed.

Excellent performance of Ce doped CoMn2O4/TiO2 catalyst in NH3-SCR of NOx under H2O&SO2 conditions

Mn-based catalysts have become a research hotspot for low-temperature NH3-SCR, and the improvement of anti-SO2 poisoning performance is crucial to promote their industrial application for NH3 selective catalytic reduction of NOx. In this work, the CoMn2O4/Ce-TiO2 catalyst was able to maintain 95 % NOx conversion even in the presence of 10 vol% H2O+50 ppm SO2 for 24 h at 250 °C.The excellent performance was attributed to the large mesoporous structure, specific surface area, and the enhancement of acid and redox properties associated with the catalysts. The Ce doped CoMn2O4/Ce-TiO2 catalyst maintained Mn3+, Mn4+ and Co3+ in high concentrations on the surface, which improved the lattice oxygen mobility, and the electron transfer and interaction. The presence of more Ce4+ provided higher SCR activity due to the strong oxygen storage migration and also release ability. The reaction process of NH3-SCR for NOx removal on the surface of CoMn2O4/Ce-TiO2 catalyst mainly followed the Eley-Rideal (E-R) mechanism. The NH3 adsorbed on the catalyst surface reacted mainly with NO/NO2 species, even under H2O&SO2. The E-R reaction mechanism on the surface of CoMn2O4/Ce-TiO2 catalyst was less restricted by the inhibition of H2O&SO2. This is one of the primary reasons for the superior anti-sulfur toxicity performance of the catalyst. This work opens a new avenue for the design of efficient and environmentally friendly NH3-SCR catalysts with good application prospects.

Selective catalytic reduction of NOx by NH3 at low temperature over Mn0.5Zr(0.5-x)Fex catalyst with different Fe/Zr ratios

ABSTRACT Through a basic co-precipitation technique, a series of Mn0.5Zr(0.5-x)Fex ternary oxide catalysts with different Fe/Zr ratios have been prepared and applied to the selective catalytic reduction of NOx. The results of catalytic activity test show that the Mn0.5Zr0.2Fe0.3 catalyst with a molar ratio of Fe/Zr of 3:2 has the most effective denitrification activity at low temperature and displays considerable tolerance to SO2 and H2O. The Mn0.5Zr0.2Fe0.3 catalyst exhibits a combination of physical and chemical attributes, including an elevated specific surface area and a homogeneously distributed active component, which collectively furnish additional points of interaction for the reacting gases, thus improving the catalytic performance. In addition, the high Mn4+/Mnn+ and Fe2+/Fen+ ratios, strong redox capacity, and more acidic sites on the surface of the catalyst also have positive effects on its denitrification performance. Meanwhile, the reaction process on Mn0.5Zr0.2Fe0.3 catalyst is driven by the Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms. This study provides an important reference for the design of Mn-based catalysts with high denitration performance and excellent resistance to SO2 and H2O.

Contrasting Metallic (Rh0) and Carbidic (2D-Mo2C MXene) Surfaces in Olefin Hydrogenation Provides Insights on the Origin of the Pairwise Hydrogen Addition.

Kinetic studies are vital for gathering mechanistic insights into heterogeneously catalyzed hydrogenation of unsaturated organic compounds (olefins), where the Horiuti-Polanyi mechanism is ubiquitous on metal catalysts. While this mechanism envisions nonpairwise H2 addition due to the rapid scrambling of surface hydride (H*) species, a pairwise H2 addition is experimentally encountered, rationalized here based on density functional theory (DFT) simulations for the ethene (C2H4) hydrogenation catalyzed by two-dimensional (2D) MXene Mo2C(0001) surface and compared to Rh(111) surface. Results show that ethyl (C2H5*) hydrogenation is the rate-determining step (RDS) on Mo2C(0001), yet C2H5* formation is the RDS on Rh(111), which features a higher reaction rate and contribution from pairwise H2 addition compared to 2D-Mo2C(0001). This qualitatively agrees with the experimental results for propene hydrogenation with parahydrogen over 2D-Mo2C1-x MXene and Rh/TiO2. However, DFT results imply that pairwise selectivity should be negligible owing to the facile H* diffusion on both surfaces, not affected by H* nor C2H4* coverages. DFT results also rule out the Eley-Rideal mechanism appreciably contributing to pairwise addition. The measurable contribution of the pairwise hydrogenation pathway operating concurrently with the dominant nonpairwise one is proposed to be due to the dynamic site blocking at higher adsorbate coverages or another mechanism that would drastically limit the diffusion of H* adatoms.

Enhancing Water Tolerance and N2 Selectivity in NH3-SCR Catalysts by Protecting Mn Oxide Nanoparticles in a Silicalite-1 Layer.

Mn-based catalysts are promising candidates for eliminating harmful nitrogen oxides (NOx) via selective catalytic reduction with ammonia (NH3-SCR) due to their inherent strong redox abilities. However, poor water tolerance and low N2 selectivity are still the main limitations for practical applications. Herein, we succeeded in preparing an active catalyst for NH3-SCR with improved water tolerance and N2 selectivity based on protecting MnOx with a secondary growth of a hydrophobic silicalite-1. This protection suppressed catalyst deactivation by water adsorption. Interestingly, impregnating MnOx on MesoTS-1 followed by silicalite-1 protection allowed for a higher dispersion of MnOx species, thus increasing the concentration of acid sites. Consequently, the level of N2O formation is decreased. These improvements resulted in a broader operating temperature of NOx conversion and a modification of the NH3-SCR mechanism. Diffuse reflectance infrared Fourier transform spectroscopy analysis revealed that unprotected Mn/MesoTS-1 mainly followed the Eley-Rideal mechanism, while Mn/MesoTS-1@S1 followed both Langmuir-Hinshelwood and Eley-Rideal mechanisms.

Synergistic catalysis of NO and chlorobenzene over Mn3O4-CeO2 catalysts: Acid sites, catalytic pathway and mechanism

Catalyst active sites and surface acidity are crucial for the synergistic catalysis of NOx and dioxins, determining the selectivity towards N2 and CO2. This study synthesized Mn3O4-CeO2 catalysts to investigate the influence of these sites on the catalytic performance for NO and chlorobenzene. Mn0.086Ce, made by the redox method, showed the highest Mn-Ce interface, achieving nearly complete conversion of chlorobenzene and NO at 180℃, with CO2 and N2 selectivity reaching about 80 % and 100 %, respectively. EPR, NH3-TPD and Py-IR analyses revealed that the Mn-Ce interface induces the formation of Lewis acid sites and oxygen vacancies, facilitating the adsorption and conversion of chlorobenzene, NH3, and NO. Mn adjacent to Lewis acid sites is the main active site, while Ce acts as an electron transfer agent. Based on the results of in-situ DRIFTS and TOF-SIMS, the possible degradation pathway for chlorobenzene was proposed and as follows: phenol, benzoquinone, maleic anhydride, propionic acid, CO2, and H2O. The NH3-SCR reaction follows the Eley-Rideal mechanism at 150–300℃.

Enabling high throughput deep reinforcement learning with first principles to investigate catalytic reaction mechanisms

Exploring catalytic reaction mechanisms is crucial for understanding chemical processes, optimizing reaction conditions, and developing more effective catalysts. We present a reaction-agnostic framework based on high-throughput deep reinforcement learning with first principles (HDRL-FP) that offers excellent generalizability for investigating catalytic reactions. HDRL-FP introduces a generalizable reinforcement learning representation of catalytic reactions constructed solely from atomic positions, which are subsequently mapped to first-principles-derived potential energy landscapes. By leveraging thousands of simultaneous simulations on a single GPU, HDRL-FP enables rapid convergence to the optimal reaction path at a low cost. Its effectiveness is demonstrated through the studies of hydrogen and nitrogen migration in Haber-Bosch ammonia synthesis on the Fe(111) surface. Our findings reveal that the Langmuir-Hinshelwood mechanism shares the same transition state as the Eley-Rideal mechanism for H migration to NH2, forming ammonia. Furthermore, the reaction path identified herein exhibits a lower energy barrier compared to that through nudged elastic band calculation.

The effect of SO2 on NH3-SCR reaction synergistic CO oxidation over a Mn-Co-Ti catalyst

Mn–Co–TiO2 prepared using an impregnation method was applied to synergistic NH3-based selective catalytic reduction (NH3-SCR) and CO oxidation in a simulated flue gas. The NO conversion, NO oxidation, and CO oxidation were substantially enhanced after adding 15% Co3O4 to the 20MnTi catalyst. In an NO or NO + NH3 atmosphere, CO oxidation over the Mn–Co–TiO2 catalyst was mainly restrained by the competitive adsorption and formation of sulfate species. In contrast, the NH3-SCR reaction progressed almost unimpeded in a CO atmosphere. A SO2 atmosphere drastically reduced the NO conversion of the catalyst at lower temperatures and almost completely suppressed the oxidation activities toward NO and CO. The amount of remaining NO oxidation (approximately 10%) was primarily contributed by gas-phase oxidation of NO by O2. Next, fresh and SO2-poisoned Mn–Co–TiO2 were characterized using various methods. Results indicated that no conspicuous change occurred in the crystal structure of the samples after SO2 poisoning, but numerous sulfate products were deposited on the catalyst surface. The deposition of sulfate-species byproducts decreased the specific surface area and pore volume of the catalyst and shifted the surface acid sites to a higher temperature range, further reducing the CO oxidation performance. Moreover, the catalytic reaction of CO and NO followed the Eley–Rideal mechanism. Furthermore, the mechanisms through which multicomponent flue gases influence the synergistic NH3-SCR and CO oxidation performance were proposed.

Effects of MOx modification (M = Mn, Ce, and Fe) on the SCR catalytic properties of the CrOx-WOx mixed oxide catalysts

In this study, a series of MOx-modified (M = Mn, Fe, and Ce) CrOx-WOx mixed oxides were synthesized via the sol-gel technique for the selective catalytic reduction of NOx with NH3. Given the addition of MnOx or CeOx, the availability of the catalyst surface acid sites tended to decline, which negatively affected the proceeding of the deNOx process. Moreover, the retention of oxidative ability by introducing MnOx also favored the over-oxidation of NH3, which accelerated the additional formation of NOx and created a crucial barrier for the increment in the higher-temperature deNOx activity. Apparently, <80 % of the NOx could be effectively eliminated from the working gas within the whole temperature range for the CrCeW and CrMnW samples. By contrast, doping FeOx was able to introduce ample acid sites onto the catalyst surfaces, which was beneficial for the adsorption of NH3 and subsequently the facilitation of the progression of the deNOx process. Furthermore, the weakened oxidizability suppressed the over-oxidation of NH3. Consequently, a broad operating temperature window was obtained for the FeOx-doped catalyst; >90 % NOx conversion efficiency was achieved in the temperature range of 230–450 °C. During the deNOx process, the Eley-Rideal mechanism dominated over the four investigated samples.

Behaviour of Pt10-xRux/C catalysts towards the hydrogen oxidation reaction in acidic medium in the presence of adsorbed CO

Pt10-xRux/C materials are synthesised using a classical polyol method and comprehensively characterised by thermogravimetric analysis, inductively coupled plasma – optical emission spectroscopy, electron transmission microscopy and x-ray diffraction. In N2-saturated electrolyte, the PtRu/C catalysts display lower onset potentials for adsorbed CO (COads) removal than the pure Pt/C one. Although the surface coverages of Pt by Ru are high, the PtRu/C catalysts display higher activity than the Pt/C one towards the hydrogen oxidation reaction (HOR), but the same mechanism occurs on all the catalysts. However, when the surface of the catalysts is saturated by COads, the HOR starts at a lower potential on Pt/C than on PtRu/C; Pt/C displays higher activity toward the HOR in the presence of COads between 0.40 and 0.55 V vs RHE. On Pt/C, a small part of COads desorbs into CO2 from 0.40 V through an Eley-Rideal mechanism, freeing very active Pt sites for the HOR. For potentials higher than 0.55 V vs RHE, the PtRu/C catalysts display higher activity for COads removal through the bifunctional mechanism. Ru atoms also block the most active Pt sites for the COads removal and the HOR.