Eley-Rideal Mechanism Research Articles

The combination poisoning effect of KCl and ZnCl2 on V2O5-WO3/TiO2deNOx catalyst

V2O5-WO3/TiO2 catalyst was used to NH3-SCR technology to control NOx emission from the waste incineration plants. While the flue gas always contains toxic substances, which resulting in the deactivation of catalysts. Most studies only reported the toxic effect of one single component. Actually, the flue gas contains multiple toxic components. Hence, the effect of combination poisoning of KCl and ZnCl2 on the activity and physicochemical properties of V2O5-WO3/TiO2 catalyst were analyzed to reveal the structure-activity relationship of the catalyst. The activity results showed that the co-existence of KCl and ZnCl2 would aggravate the toxic effect. The characterization results showed that K+, Zn2+, and Cl– would bond with V-OH and OV active sites, thereby destroying active acid sites (V-OH) and V5+⇄V4+ redox cycle. In which, KCl had a greater negative effect on active acid sites (V-OH), while ZnCl2 had a greater negative effect on the redox sites (OV). The active acid sites and redox sites on the surface of V2O5-WO3/TiO2 catalyst were further destroyed when KCl and ZnCl2 was co-existence. Moreover, the co-existence of KCl and ZnCl2 would promote the formation of stable and low-activity nitrates and nitro species, thereby inhibiting NOx participation in NH3-SCR reaction. Eley-Rideal (E-R) mechanism exists on V2O5-WO3/TiO2 catalyst, and the combination poisoning of KCl and ZnCl2 does not change the reaction mechanism.

The reduction of copper in LaFeO3, La2CuO4 and CuO three-phase system improves the efficiency of NO removal: Experimental and density functional theory calculation

Hollow spherical LaCu0.5Fe0.5O3 (LCF) and La0.8Ce0.1Cu0.5Fe0.5O3 (LCCF) catalysts are synthesized by solvothermal method, and CuO is reduced in two samples, so that the two corresponding multiphase catalysts (R-LCF and R-LCCF) were prepared and used for the selective catalytic reduction of NO with CO (CO-SCR). The results show that the balance of Ce3++Cu2+↔Cu++Ce4+ between Ce and Cu ions promotes the reduction of CuO in the Ce-doped LCCF catalyst more obviously. In addition, the reduction of Ce and Cu in R-LCCF generates more oxygen vacancies, which leads to more surface adsorbed oxygen species, thus facilitating the conversion of more NO to NOx species. Besides, the presence of reduced Cu is highly active and can inhibit the production of carbonates occupying the active site. The ability to activate both CO and NO after the evolution of Cu0 to the key species Cu+ leads to a rapid reaction between Cu+-CO and NOx species. These are the key factors for the significant increase in catalytic activity at low temperatures. It is worth noting that the CO-SCR reaction on the R-LCCF catalyst corresponds to the Langmuir-Hinshlwood (L-H) and Eley-Rideal (E-R) mechanisms at different temperature windows, respectively.

Migration and transformation mechanisms of Pb/Cd with HCl in organic solid waste incineration flue gas on the composite-modified kaolinite surface

Cadmium/lead (Cd/Pb) pollutants from organic solid wastes (OSW) incineration are of global concern due to high volatility and biotoxicity. The strong interaction between modified kaolinite and Cd/Pb species inspires its utilization for the elimination of heavy metals. However, the specific mechanism of the migration and transformation of Cd/Pb species is yet unclear. Consequently, the migration and transformation mechanisms of Cd/Pb species on the modified kaolinite (001) surface are examined by density functional theory (DFT), considering the effect of HCl. The outcomes show that the HCl significantly alters the characteristics of the kaolinite, which enhances the surface activity of kaolinite and promotes the adsorption and transformation of Cd/Pb species. Furthermore, the chlorination routes of Cd0/Pb0 are fully elucidated in both 2-step and 1-step routes. The first step of the 2-step route obeys the Langmuir-Hinshelwood mechanism and the second step obeys the Eley-Rideal mechanism, while the 1-step chlorination route obeys the Eley-Rideal mechanism. In addition, the oxidation route of Cd0/Pb0 follows the Mars-van Krevelen mechanism. The comparison of the energy barriers shows that the 1-step Cd0/Pb0 chlorination route has the lowest energy barrier. The kaolinite surface is found to have elevated activity for the adsorptive trapping of Cd/Pb species in the presence of HCl, which offers a preliminary theoretical framework for pollutant control on the modified kaolinite surface.

Catalytic Oxidation of Chlorobenzene over HSiW/CeO2 as a Co-Benefit of NOx Reduction: Remarkable Inhibition of Chlorobenzene Oxidation by NH3.

There is an urgent need to develop novel and high-performance catalysts for chlorinated volatile organic compound oxidation as a co-benefit of NOx. In this work, HSiW/CeO2 was used for chlorobenzene (CB) oxidation as a co-benefit of NOx reduction and the inhibition mechanism of NH3 was explored. CB oxidation over HSiW/CeO2 primarily followed the Mars-van-Krevelen mechanism and the Eley-Rideal mechanism, and the CB oxidation rate was influenced by the concentrations of surface adsorbed CB, Ce4+ ions, lattice oxygen species, gaseous CB, and surface adsorbed oxygen species. NH3 not only strongly inhibited CB adsorption onto HSiW/CeO2, but also noticeably decreased the amount of lattice oxygen species; hence, NH3 had a detrimental effect on the Mars-van-Krevelen mechanism. Meanwhile, NH3 caused a decrease in the amount of oxygen species adsorbed on HSiW/CeO2, which hindered the Eley-Rideal mechanism of CB oxidation. Hence, NH3 significantly hindered CB oxidation over HSiW/CeO2. This suggests that the removal of NOx and CB over this catalyst operated more like a two-stage process rather than a synergistic one. Therefore, to achieve simultaneous NOx and CB removal, it would be more meaningful to focus on improving the performances of HSiW/CeO2 for NOx reduction and CB oxidation separately.

Heteroatoms doped iron oxide-based catalyst prepared from zinc slag for efficient selective catalytic reduction of NOx with NH3

Excessive emissions of nitrogen oxides from flue gas have imposed various detrimental impacts on environment, and the development of deNOx catalysts with low-cost and high performance is an urgent requirement. Iron oxide-based material has been explored for promising deNOx catalysts. However, the unsatisfactory low-temperature activity limits their practical applications. In this study, a series of excellent low-temperature denitrification catalysts (Ha-FeOx/yZS) were prepared by acid treatment of zinc slag, and the mass ratios of Fe to impure ions was regulated by adjusting the acid concentrations. Ha-FeOx/yZS showed high denitrification performance (> 90%) in the range of 180–300 °C, and the optimal NO conversion and N2 selectivity were higher than 95% at 250 °C. Among them, the Ha-FeOx/2ZS synthesized with 2 mol/L HNO3 exhibited the widest temperature window (175–350 °C). The excellent denitrification performance of Ha-FeOx/yZS was mainly attributed to the strong interaction between Fe and impurity ions to inhibit the growth of crystals, making Ha-FeOx/yZS with amorphous structure, nice fine particles, large specific surface area, more surface acid sites and high chemisorbed oxygen. The in-situ DRIFT experiments confirmed that the SCR reaction on the Ha-FeOx/yZS followed both Langmuir-Hinshelwood (L-H) mechanism and Eley-Rideal (E-R) mechanism. The present work proposed a high value-added method for the preparation of cost-effective catalysts from zinc slag, which showed a promising application prospect in NOx removal by selective catalytic reduction with ammonia.

Leveraging Expertise in Thermal Catalysis to Understand Plasma Catalysis.

Best practices in testing heterogeneous catalysts are translated to plasma-catalytic experiments. Independent determination of plasma-catalytic and plasma-chemical contributions is essential. Non-porous catalyst particles are preferred because active sites inside sub-micron pores cannot contribute. Temperature variation is needed to determine kinetics, despite the complexity of thermal effects in plasma. Rigorous checks on catalyst deactivation and mass balance are needed. Plasma enhanced reversed reactions should be minimized by keeping conversion low and far from thermodynamic equilibrium, preventing underestimation of the rate of forward reaction. In contrast, plasma-catalytic studies often aim at conversions surpassing thermodynamic equilibrium, not obtaining any information on kinetics. Calculation of catalyst activity per active sites (turn-over-frequency) requires also appropriate characterization to determine the number of active sites. The relationship between kinetics and thermodynamics for plasma-catalysis is discussed using endothermic decomposition of CO2 and exothermic synthesis of ammonia from N2 and H2 as examples. Assuming Langmuir-Hinshelwood and Eley-Rideal mechanisms, the effect of excitation of reactant molecules on activation barriers and surface coverages are discussed, influencing reaction rates. The consequences of reversed reactions are considered. Plasma-catalysis with catalysts applied for thermal catalysis at much higher temperature should be avoided, as adsorbed species are bonded too strongly resulting in low rates.

Increasing the Catalytic Activity of Co3O4 via Boron Doping and Chemical Reduction for Enhanced Acetone Detection

AbstractOptimally increasing the catalytic activity of Co3O4‐based materials is crucial for promoting their practical applications for acetone detection; however, this still remains challenging. Herein, a strategy is proposed in this work to increase the catalytic activity of Co3O4 toward the oxidation of acetone through the synergistic effect of boron doping and chemical reduction, which can substantially improve the sensing performance for acetone detection. The characterization results confirm that the present strategy facilitates the formation of more oxygen vacancies and increases the content of Co2+ ions serving as active sites. As expected, the optimal sensor yields a higher response . To extend the practical application to the auxiliary diagnosis of diabetes through exhaled breath, the optimal sensors distinguished between acetone concentrations in the breath of healthy individuals and in the simulated breath of patients with diabetes. Detailed gas‐sensing measurements reveal that the enhanced acetone sensing performance is attributed to the increased catalytic activity of materials for oxidation of acetone by the Mars–van Krevelen, Langmuir–Hinshelwood, and Eley–Rideal mechanisms. This study provides new insights into the fabrication of high‐performance metal oxide‐based gas sensors by improving the catalytic activity of sensing materials.

Gd-modified Mn-Co oxides derived from layered double hydroxides for improved catalytic activity and H2O/SO2 tolerance in NH3-SCR of NOx reaction

Metal oxides derived from layered double hydroxides (LDHs) are expected to obtain low-temperature denitrification (de-NOx) catalysts with high catalytic activity and H2O/SO2 tolerance in the selective catalytic reduction (SCR) of NOx with NH3. In current work, we successfully prepared Gd-modified Mn-Co metal oxides derived from Gd-modified Mn-Co LDHs. The resultant Gd-modified Mn-Co metal oxides exhibit excellent catalytic activity and high H2O/SO2 tolerance in the NH3-SCR de-NOx reaction. The reasons for the enhancement can be ascribed to the unique surface physicochemical properties inherited from LDHs and the modification of Gd, which increase the specific surface area, improve the relative content of Mn4+ and Co3+ on the surface, enhance the number of acidic sites, strengthen the reducibility of catalyst, resulting in the enhanced catalytic activity and H2O/SO2 tolerance. Additionally, it is demonstrated that the NH3-SCR de-NOx reaction occurred on the surface of Gd-modified Mn-Co oxides followed both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms. This study provides us with a design approach to promote catalytic activity and H2O/SO2 tolerance through morphology control and rare earth modification.

Investigating NH3-SCR coupled with CO oxidation reaction mechanisms on titanium nanotube-loaded CuMnFe composite metal catalysts

NOx and CO are the primary air pollutants emitted from sintering flue gas, and their effective treatment is crucial. However, achieving good N2 selectivity with the CuMnFe composite metal oxide catalyst alone is challenging due to its oxidizing nature. Hence, in this study, titanium dioxide nanotubes were employed as carriers for the catalyst. CuMnFe composite metal oxide catalysts supported on titanium dioxide nanotubes were prepared using the co-precipitation method. The optimized catalysts demonstrated excellent performance, maintaining over 90% conversion of NOx and CO at low temperatures ranging from 120 to 200 ℃. Furthermore, significant improvement in N2 selectivity was achieved using these catalysts. Characterization results revealed several positive effects of incorporating titanium dioxide nanotube carriers into the catalyst. Firstly, it efficiently reduced the mobility of adsorbed oxygen on the catalyst surface, thus decreasing its oxidation capacity. Secondly, the addition of carriers helped balance the acidity on the catalyst surface, leading to an increase in Lewis acid sites. These modifications in the catalyst's surface properties proved advantageous for the selective catalytic reduction reaction. Moreover, the mechanisms of NH3-SCR and CO oxidation over the catalysts were extensively studied using DRIFTS. The results demonstrated that the CO oxidation reaction followed the Mars-van Krevelen mechanism, with a competitive adsorption relationship observed between O2 and CO at the active sites. On the other hand, the NH3-SCR reaction primarily followed the Eley-Rideal mechanism, with minimal occurrence of the Langmuir-Hinshelwood mechanism in the SCR reaction. The presence of NH3 inhibits CO adsorption at the active site, resulting in decreased CO oxidation performance in the NH3-SCR-coupled CO oxidation reaction at low temperatures. Nevertheless, NH3-SCR can enhance NO conversion by utilizing some of the latent heat generated from the exothermic CO oxidation.

Insight into the reasons for enhanced NH3-SCR activity and SO2 tolerance of Mn-Co layered oxides

Mn-based catalysts have a fatal flaw in selective catalytic reduction (SCR) of NOx with NH3, which is poor SO2 tolerance. In this work, we successfully fabricated Mn-Co layered double oxides (LDOs) by calcining the Mn-Co layered double hydroxides (LDHs) generated by a hydrothermal method using urea solution. The obtained Mn-Co LDO presents excellent catalytic activity and SO2 tolerance in the SCR reaction of NOx with NH3. The enhanced activity can be attributed to the special surface physicochemical properties endowed by its LDO structure, such as large specific surface area, more exposed active sites, relatively high Mn4+ and Oα/(Oα + Oβ) percentage, good reducibility, and abundant acidic sites. The enhanced SO2 tolerance can be ascribed to the weak adsorption energy of SO2 on Mn-Co LDO, which makes it difficult for SO2 to interact with the active sites. Furthermore, the NH3-SCR of NOx reaction that occurs on the surface of the MnCo-LDO follows both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms. This study shines light on the design of Mn-based de-NOx catalysts with excellent SO2 tolerance.

Kinetics of microwave-assisted synthesis of ethyl hexanoate by using heterogeneous catalyst: process intensification and energy consumption analysis

The current work illustrates microwave-assisted synthesis of ethyl hexanoate without a solvent system using cationic resin (Amberlyst-15) as a catalyst. The effect of various parameters was evaluated, and a maximum equilibrium conversion of 84.2% was achieved in 50 min. The optimized parameters were 1:02 mole ratio of acid to alcohol, temperature 328 K, and 9% (w/w) catalyst loading. The impact of mole ratio and catalyst loading on the reaction rate was predicted by developing an empirical correlation. The activation energy was determined as 17.63 kJ/mol. The experimental data fitted well with Eley-Rideal mechanism, in which the surface reaction was a rate-limiting step. Thermodynamic parameters were evaluated, including standard enthalpy, Gibbs free energy, and reaction entropy. The energy consumption for microwave reaction was predicted as 15.357 × 105 kJ/kg. These results have been compared with that of conventional as well as ultrasound-assisted synthesis of ethyl hexanoate. This novel technique shows an enhancement in reaction rates and higher yields.

Rare Earth Metal (La, Ce, Nd, Eu) Doped Cu/Zr-PILC Catalysts for the Efficient NH3-SCR at Low Temperature

ABSTRACT A series of RE-3Cu/Zr-PILC (RE = La, Ce, Nd, Eu) catalysts were prepared via an impregnation method and activities for NH3-SCR were evaluated. The physicochemical properties of each catalyst were explored using XRD, BET, H2-TPR, NH3-TPD, XPS and in-situ DRIFTS techniques. The doping of RE had enhanced the NH3-SCR efficiency of 3Cu/Zr-PILC. Among them, the 6Ce-3Cu/Zr-PILC sample demonstrated exceptional performance, achieving NO conversion rates exceeding 90% within the temperature range of 250–350°C. Moreover, it reached its peak NO conversion rate of 96.3% at 300°C while maintaining an impressive resistance to SO2. According to the results of TPR, TPD and XPS analysis, the modification of RE (especially Ce) enhanced the redox properties, the surface acidity, the atomic ratio of Cu2+/Cu+ and the amount of surface chemisorbed oxygen in the 3Cu/Zr-PILC samples, all of these are favorable for the NH3-SCR reaction. Furthermore, in-situ DRIFTS analysis reveals that the NH3-SCR reaction of RE-3Cu/Zr-PILC samples at low temperatures is governed by the Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms, with the L-H mechanism being the predominant factor.

Copper/Nickel/Cobalt modified molybdenum-tungsten-titanium dioxide-based catalysts for multi-pollution control of nitrogen oxide, benzene, and toluene: Enhanced redox capacity and mechanism study

Previous studies have indicated the potential of monometallic-modified TiO2 catalysts in controlling nitrogen oxide (NOx) and volatile organic compounds (VOCs) in coal-fired flue gas. Unfortunately, increasing selective catalytic reduction (SCR) activity under complicated coal-fired flue gas status is tricky. In this study, modified Co-MoWTiO2 catalysts with multiple active sites were synthesized using the wet impregnation method, which exhibited excellent multi-pollution control ability of NO, benzene and toluene under low oxygen and high SO2 concentrations. The modification of Mo and Co achieved high dispersion and electron transfer. The interaction between W5+/W6+ and Co2+/Co3+ promoted gas-phase O2 adsorption on the catalyst surface, forming of reactive oxygen species (Oα). Density functional theory (DFT) calculations informed that the doping of Co effectively enhanced the NH3 and O2 adsorption capacity of the catalyst, and Co possessed the maximum adsorption energy for NH3 and O2. Possible pathways of multi-pollution control of NO, C6H6, and C7H8 were speculated. NH3/NH4+ on the Lewis/Bronsted acid site is reacted with intermediates of NO (e.g., NO2, nitrite, nitrate) via the Langmuir-Hinshelwood and Eley-Rideal mechanism. The introduction of NO and NH3 did not disrupt the oxidation pathways of benzene and toluene. Following the Mars-van Krevelen mechanism, C6H6 and C7H8 were progressively mineralized by Oα into CO2 and H2O.

Enhanced dual-catalytic elimination of NO and VOCs by bimetallic oxide (CuCe/MnCe/CoCe) modified WTiO2 catalysts: Boosting acid sites and rich oxygen vacancy

It remains challenging to remove nitrogen oxides (NOx), benzene (C6H6), and toluene (C7H8) simultaneously under conditions of low oxygen and high SO2 concentration. Herein, CuCe, MnCe, and CoCe doped WTiO2 catalysts were designed. The prepared CuCe-WTiO2 catalyst consistently maintained more than 85% NO, 92% C6H6, and 91% C7H8 removal in 260–420 °C under 3.33% O2 and 1000 ppm SO2. The adequate charge flow between the catalyst surface and the gas molecules was enhanced, promoting SO2 tolerance of CuCe-WTiO2. More NH3, NH4+, and -NH2 were adsorbed with acid sites on the CuCe-WTiO2 surface. The high concentration of adsorption centers and superior redox properties effectively improved the co-catalytic efficiency. The primary intermediates in the reduction processes via the Langmuir-Hinshelwood and Eley-Rideal mechanisms were NO2, bridged nitrite (NO2–), and monodentate nitrite (NO2–). The generation of reactive chemisorbed oxygen (Oα) becomes more accessible with the transfer of electrons from Ce4+ to adsorbed O2. C6H6 and C7H8 are progressively oxidized by Oα and eventually completely mineralized to CO2 and H2O. This study is anticipated to offer a new option for co-catalytic removal of NO, C6H6, and C7H8.

Highly dispersed V2O5-WO3 in modified morphology of flower-like TiO2 for NH3-selective catalytic reduction over wide temperatures

NOX, a first-class carcinogen, and secondary particulate matter are produced in Various industrial processes form stationary sources such as steel mills and thermal power plants. Selective catalytic reduction is a method of repeatedly exposing used as V2O5-WO3/TiO2 to high temperatures by used NH3 reduction agent to N2 and H2O. Consequently, the catalytic performance decreases during the aggregation of transition metal and support, and industries need catalysts that react in a wide temperature range. In this study, flower-type TiO2 (FL-Ti) that changes the morphology of TiO2 was synthesized through hydrothermal method, anatase TiO2 with a similar specific surface area to commercial TiO2 was synthesized, and the dispersibility of transition metals was increased. Synthesis was conducted by changing the ratio of commercial TiO2 to FL-Ti to increase economic efficiency and reduce aggregation of transition metal and TiO2, thus resulting in their high dispersion. The presence of Ti3+ in FL-Ti increased the hydroxyl group owing to increased Ti-O bonds and the V4+ ratio, which positively influenced the catalyst at low temperatures. The catalyst with added FL-Ti reacted with the Eley-Rideal mechanism. Additionally, NOX conversion and N2 selectivity were approximately 93–99% at temperatures ranging from 250–420 ℃.

A theoretical study into the performance of DACs loaded on MgO utilized in CO oxidation

Single-atom catalysts (SACs) have garnered significant attention due to their unique combination of advantages from both heterogeneous and homogeneous catalysts. However, SACs composed of just one metal cannot adequately meet the various catalytic requirements. Thus, this study focused on the addition of a second metal atom to M1/MgO systems (M = Au, Ag and Cu) to create dual-atom catalysts (DACs) supported on different di-vacancy types on MgO(100) surfaces. Homogeneous (Au2, Ag2, Cu2) and multiphase (Au1Ag2, Au1Cu2 and Ag1Cu2) were analyzed for their selectivity in CO oxidation by Langmuir-Hinshaw (LH) and Eley-Rideal (ER) mechanisms using density functional theory (DFT) method. The results indicated that the tri-molecules ER pathway had the highest selectivity, and the multiphase DACs had better CO catalytic oxidation activity compared to homogeneous DACs. Among all multiphase DACs in the tri-molecules ER pathway, alloy DACs of Au1Ag2/MgO(Fc-Fc) and Au1Cu2/MgO(Fc-Vc) had the lowest energy barrier for CO oxidation, and the addition of a second metal atom improved stability compared to SAC of Au1/MgO(Fc). DFT calculations combined with microkinetic simulations revealed that under reaction conditions, Au1Cu2/MgO(Fc-Vc) had a remarkably high TOF of CO2, making it a promising DAC for practical applications. This study provides valuable insights into the development of efficient and low-cost atomic-scale catalysts.

Highly efficient MnCe/Ti catalyst for NH3-SCR of NO from sintering flue gas at low temperature: CO tolerance and reaction mechanism assessed by in situ DRIFTS

The effect of metal doping (Ce, Fe, and Co) on CO tolerance of Mn/Ti catalyst used for eliminating NO from sintering flue gas has been investigated. The best MnCe/Ti catalyst achieves a NOx conversion of 80 % from 125 to 250 °C at a GHSV of 80,000 h−1. NOx conversion dropped by only 4 % below 200 °C and N2 selectivity slightly increased after introduction of CO, indicating strong resistance of MnCe/Ti catalyst to CO. XPS results suggest that CO oxidation does not alter surface content of Mn4+ and Ce3+ sites of used MnCe/Ti catalyst while it reduces the surface adsorbed oxygen of used MnCe/Ti catalyst because surface adsorbed oxygen consumed by CO oxidation cannot be readily replenished owing to the insufficient capacity in oxygen and electron transport. This is primarily accountable for the slight decrease in NOx conversion. Furthermore, NH3 can completely restrain CO adsorption on MnCe/Ti catalyst while CO cannot hinder the adsorption of NH3 and NO on the catalyst because the interaction between CO and MnCe/Ti catalyst significantly weakened in the presence of NH3, leading to the strong CO tolerance of MnCe/Ti. On MnCe/Ti Eley-Rideal mechanism governs the NH3-SCR involving gaseous NO and adsorbed NH3, while Mars-van Krevelen mechanism describes the oxidation of CO, indicating its reaction with gaseous CO and surface adsorbed oxygen. The findings in this paper can provide modification strategy for low-temperature SCR catalysts which are expected to be applied for sintering flue gas.

Effect of Fe2O3 on ZrTiO4 support for NH3-SCR catalytic performance

The selective catalytic reduction (SCR) NH3 catalyst is mainly used in industrial production and automobile exhaust cleaning. In this study, a novel α%Fe2O3/ZrTiO4 (α=0, 8, 12, 15) catalyst was prepared by the coprecipitation impregnation method. The results show that the NOx conversion rate of 12%Fe2O3/ZrTiO4 catalyst with the optimal composition is high above 80% at 250−400 °C, close to 100% at 300 °C, and N2 selectivity is high above 90% at 200−450 °C. The redox properties, surface acidity, and Oβ/(Oα + Oβ) ratio of ZrTiO4 catalysts are improved after loading Fe2O3 on the ZrTiO4 surface, which is attributed not only to the porous structure of α%Fe2O3/ZrTiO4 catalyst but also to the synergistic interaction between the active component Fe2O3 and the support ZrTiO4. In addition, in-situ DRIFT reactions show that the NH3-SCR reaction of 12%Fe2O3/ZrTiO4 catalyst follows the Eley-Rideal mechanism. A clear reaction mechanism is conducive to a deeper understanding of the reaction process of NOx conversion during SCR. This work provides a feasible strategy for Fe-based SCR catalysts to replace V-based catalysts in the medium temperature range in the future.

Low-temperature CeCoMnOx spinel-type catalysts prepared by oxalate co-precipitation for selective catalytic reduction of NO using NH3: A structure–activity relationship study

CeCoMnOx spinel-type catalysts for the selective catalytic reduction of NO using NH3 (NH3-SCR) are usually prepared by alkaline co-precipitation. In this paper, a series of CeCoMnOx spinel-type catalysts with different calcination temperatures were prepared by acidic oxalate co-precipitation. The physicochemical structures and NH3-SCR activities of the CeCoMnOx spinel-type catalysts prepared by oxalate co-precipitation and conventional ammonia co-precipitation were systematically compared. The results show that the CeCoMnOx spinel-type catalysts prepared by the oxalate precipitation method (CeCoMnOx-C) have larger specific surface area, more mesopores and surface active sites, stronger redox properties and adsorption activation properties than those prepared by the traditional ammonia co-precipitation method at 400 °C (CeCoMnOx-N-400), and thus CeCoMnOx-C have better low-temperature NH3-SCR performance. At the same calcination temperature of 400 °C, the NO conversion of CeCoMnOx-C-400 exceeds 89 % and approaches 100 % within the reaction temperature of 100–125 °C, which is 14.8 %-2.5 % higher than that of CeCoMnOx-N-400 at 100–125 °C. In addition, the enhanced redox and acid cycle matching mechanisms on the CeCoMnOx-C surface, as well as the enhanced monoadsorption Eley-Rideal (E-R) and double adsorption Langmuir-Hinshelwood (L-H) reaction mechanisms, are also derived from XPS and in situ DRIFTS characterization.

Incorporation of Ag on stable Pt/CeO2 for low-temperature active and high-temperature stable CO oxidation catalyst

Advanced engine technologies and environmental restrictions require new-generation automotive catalysts to be low-temperature (LT) active and high-temperature (HT) stable simultaneously. Here, incorporation of Ag over high temperature (800 °C) treated Pt/CeO2 was applied to address the challenge. Strong Pt-O-Ce bonds in Pt/CeO2 helped improve thermal stability dramatically. Detailed reaction kinetics analysis indicated Eley-Rideal (ER) mechanism for Ag/CeO2 catalysts and Mars-van Krevelen (Mvk) mechanism for both Pt/CeO2 and Ag/Pt/CeO2 catalyst. After calcined at 800 °C, CO adsorbed on ionic Pt site could be readily oxidized by neighbouring oxygen species at a temperature as low as 132 °C over Ag/Pt/CeO2, about 60 °C lower than Pt/CeO2 and Ag/CeO2. Raman spectroscopy and XPS results suggested that incorporation of Ag created more oxygen defects over Pt/CeO2 and oxygen species on Ag nanoparticles might be more active than bare Pt/CeO2 which would enhance the low-temperature activity for Ag/Pt/CeO2. It might be an effective and cost-efficient approach to develop new catalysts for vehicle emission oxidation.