Low-temperature Catalytic Performance Research Articles

Praseodymium-Doped Cr2O3 Prepared by In Situ Pyrolysis of MIL-101(Cr) for Highly Efficient Catalytic Oxidation of 1,2-Dichloroethane.

The development of economical catalysts that exhibit both high activity and durability for chlorinated volatile organic compounds (CVOCs) elimination remains a challenge. The oxidizing and acidic sites play a crucial role in the oxidation process of CVOCs; herein, praseodymium (Pr) was introduced into CrOx catalysts via in situ pyrolysis of MIL-101(Cr). With the decomposition of the ligand, a mixed micro-mesoporous structure was formed within the M-Cr catalyst, thereby reducing the contact resistance between catalyst active sites and the 1,2-dichloroethane molecule. Moreover, the synergistic interaction between chromium and praseodymium facilitates Oβ species and acidic sites, significantly enhancing the low-temperature catalytic performance and durability of the M-PrCr catalyst for 1,2-dichloroethane (1,2-DCE) oxidation. The M-30PrCr catalyst possess enhanced active oxygen sites and acid sites, thereby exhibiting the highest catalytic activity and stability. This study may provide a novel and promising strategy for practical applications in the elimination of 1,2-DCE.

Study on the Catalytic Activity Modification of Pr and Nd Doped Ce0.7Zr0.3O2 Catalysts for Simultaneous Removal of PM and NOX

Cerium-zirconium composite oxides (Ce0.7Zr0.3O2) have a remarkable effect on catalytic removal of carbon particles (PM) and nitrogen oxides (NOX) emitted from diesel engine, in order to further improve the thermal stability, oxygen storage capacity and low temperature catalytic REDOX performance of cerium zirconium composite oxides (Ce0.7Zr0.3O2), a small amount of Pr and Nd rare earth elements are doped to improve the catalytic activity of cerium zirconium composite oxides. In this paper, the composite oxide of Pr6O11–Nd2O3–CeO2–ZrO2 is prepared by unsteady co-precipitation method, and the physicochemical properties of the composite oxide catalyst are analyzed by BET, SEM, XRD and ICP. The gas adsorption capacity and catalytic activity of composite oxide catalysts are measured by temperature programmed reaction technology (TPR). The results show that the composite oxide of Pr0.05Nd0.05Ce0.6Zr0.3O2 prepared by using rare earth elements Pr and Nd inhibits the growth process of grain, refining the grain, and improving the sintering phenomenon at high temperature. The addition of Pr and Nd causes lattice defects, increases the number of oxygen vacancies, and improves the mobility of lattice oxygen, namely promotes oxide oxygen storage property, gas adsorption and catalytic oxidation reduction ability. After modification, Pr0.05Nd0.05Ce0.6Zr0.3O2 has good resistance to high temperature aging performance, prolongs the service life, reduces the PM lowest ignition temperature and minimum catalytic activity temperature of nitrogen oxide, and promotes the NOX reduction rate. For Pr0.05Nd0.05Ce0.6Zr0.3O2, the lowest ignition temperature of PM is about 150 °C, and the lowest catalytic activity temperature of NO is about 130 °C. The maximum CO2 production rate is 68.3%, and the maximum NO reduction rate is 45%.

Influence of anionic species on the low temperature pyrolysis performance of heated tobacco sheets catalyzed by sodium salts.

Development of low temperature catalytic pyrolysis technology for heated tobacco sheets is expected to increase the aroma of heated tobacco products and improve their overall smoking quality. In this study, the low temperature pyrolysis performances of heated tobacco sheets catalyzed by various anionic sodium salts were investigated using TG-DTG, Py-GC-MS technology and smoke routine chemical composition analysis. The results showed that the total weight loss between 100°C and 300°C increased by 7.8%-13.15% after adding various anionic sodium salts, among which, sodium acetate and sodium tartrate showed a relatively higher weight loss. The relative content of free hydroxyacetone, furfuryl alcohol, butyrolactone and megastigmatrienone in the pyrolysis gas increased, while the relative content of free nicotine decreased. With the change of anionic species, the catalytic decomposition ability of cellulose, lignin, and other substances may change, resulting in the distribution alteration of compounds in the pyrolysis gas. After adding sodium acetate and sodium citrate, the release of total particulate matter (TPM), glycerol, and nicotine in flue gas increased. Overall, the addition of sodium acetate and sodium citrate showed a higher low temperature pyrolysis performance of heated tobacco sheets. The research results in this paper provide data support for changing the low temperature catalytic pyrolysis performance of heated tobacco sheets by adjusting the type of anions in sodium salts.

Exploring the rate-control step of toluene oxidation over the novel octahedral Pt/Mn3O4 catalyst with stable low-temperature catalytic performance via in situ DRIFTS

The high efficiency and stability of catalysts are crucial for their practical application in toluene oxidation. Herein, a novel octahedral Pt/Mn3O4-110 catalyst with excellent structural stability was synthesized and 100 % toluene conversion can be achieved at low-temperature 160 °C. XRD and Raman results indicated that the structure of Pt/Mn3O4-110 can be well maintained after 120 h on-stream reaction, the resistance to H2O (3 or 5 vol%) and high concentration toluene (3000 ppm)/CO2 (5 vol%) tests. In situ DRIFTS comparative studies between Pt/Mn3O4-110 and Pt/Mn3O4-100 (30 % toluene conversion at 160 °C) samples demonstrated that the rate-control steps of toluene oxidation on Pt/Mn3O4-110 and Pt/Mn3O4-100 were both the further oxidation of benzoate species in the presence of gas-phase oxygen, while the transformation of benzaldehyde to benzoate species was the rate-control step on Pt/Mn3O4-100 in the absence of gas-phase oxygen. The weaker Mn-O bonds, richer oxygen vacancies and higher mobility of oxygen species on Pt/Mn3O4-110 sample than that of Pt/Mn3O4-100 are beneficial for the easier release of lattice oxygen from the surface of catalyst and then participated in toluene oxidation via Mars-van Krevelen mechanism, contributing to easier oxidation of benzaldehyde to benzoate species and formation of formic acid and bicarbonate species.

Synthesis of InZrOx nanosheets and its application in CO2 hydrogenation to methanol

Synthesis of methanol via CO2 hydrogenation is a very important reaction. In recent years, the In2O3 based catalysts were proved to be a sort of promising catalysts to accelerate this reaction, which have aroused extensive attention. However, design of novel In2O3 based catalysts that can efficiently produce methanol from CO2 hydrogenation at low temperature is still in great need. Herein we fabricated the InZrOx nanosheets via a simple solvothermal method, which had peculiar surface structure and plenty of oxygen defects. The InZrOx nanosheets displayed excellent low temperature catalytic performance in a slurry reactor. The methanol selectivity (90 %) and activity (1.4 mmol gIn-1h−1) were achieved at 180 °C, which are 2.3 and 1.6 times than that of the counterpart nanoparticles, respectively. Water as a clean and cheap reaction solvent played a crucial role, which participated in the kinetic process of the catalysis. The particular catalyst structure and the solvent effect of water accounting for the outstanding reaction results.

Selective dissolution of micro-spherical Ca-Mn mixed oxides for efficient propane oxidation

The improvement of catalytic efficiency is of great significance to the removal of volatile organic compounds (VOCs), a class of key air pollutants leading to ground-level ozone pollution. Herein, a series of micro-spherical Ca-Mn mixed oxides (CaxMnyOz), namely CaMn3O6, Ca2Mn3O8 and CaMnO3, were prepared by a two-step precipitation method, and defects were constructed on which by selective dissolution to enhance the low-temperature catalytic performance in the oxidation of propane (C3H8) as a representative short-chain alkane VOCs. The synthesized CaxMnyOz oxides demonstrated drastically different response to the dissolution modification initiated by acid treatment. Specifically, after acid dissolution, while CaMn3O6 and Ca2Mn3O8 maintained largely their original structures, the perovskite-type CaMnO3 underwent lattice rearrangement and was transformed into γ-MnO2-like product with only a tiny amount of Ca. In C3H8 oxidation, the catalytic performance of CaMnO3 was significantly improved after selective dissolution, as indicated by a significant decrease of T90, i.e. the temperature to achieve 90% C3H8 conversion, from 455 °C to 240 °C. Mechanistic investigation by in-depth X-ray photoelectron spectroscopy studies revealed that selective dissolution led to higher Mn4+ concentrations and more oxygen vacancies on the oxide surfaces, thus facilitated electron transfer and O2 activation in C3H8 oxidation reactions. This study paves a new path for the design of cost-effective oxide catalysts toward the abatement of short-chain alkane VOCs.

Construction of unique oxygen vacancy defect through various metal-doping (Cu, Mn, Zr) of Ce2Co1Ox nanoparticles towards boosting the catalytic oxidation toluene performance

Achievement of catalytic oxidation of volatile organic compounds (VOCs) at low temperature is still a challenge to be addressed. Promoting catalytic activity via constructing oxygen vacancy defect is an attractive strategy in heterogeneous catalysis. Herein, a series of Ce2Co1M1 (M = Cu, Mn, Zr) catalysts were prepared by modified co-precipitation method and their catalytic oxidation performance of toluene was measured. Activity results suggested that the introduction of doping-metals significantly enhanced the catalytic performance of Ce2Co1Ox, with Ce2Co1Cu1 possessed the optimal catalytic activity (T90 = 210 ℃), robust stability, water resistance, GHSV tolerance and anti-aging ability. It has been demonstrated that Cu-doping resulted in the formation of Cu-Ce solid solution and constructed a Cu2+-O-Ce4+ complex active site. Benefiting from this, the redox and gaseous oxygen molecule capture & activation capabilities of the catalyst are tremendously improved via constructing abundant oxygen vacancies. The in-situ DRIFTS results revealed that Ce2Co1Cu1 exhibited a better C=C breaking of aromatic rings ability, a faster consumption rate of benzoate and maleic anhydride, and is less prone to accumulation of by-products, the above account for its enhanced low-temperature catalytic performance for toluene. This work may provide a new strategy to design the high-efficiency toluene oxidation catalysts.

Low-temperature redox activity and alcohol ammoxidation performance on Cu- and Ru-incorporated ceria catalysts.

Transition-metal-incorporated cerium oxides with Cu and a small amount of Ru (Cu0.18Ru0.05CeOz) were prepared, and their low-temperature redox performance (<423 K) and catalytic alcohol ammoxidation performance were investigated. Temperature-programmed reduction/oxidation under H2/O2 and in situ X-ray absorption fine structure revealed the reversible redox behavior of the three metals, Cu, Ru, and Ce, in the low-temperature redox processes. The initially reduced Ru species decreased the reduction temperature of Cu oxides and promoted the activation of Ce species. Cu0.18Ru0.05CeOz selectively catalyzed the production of benzonitrile in the ammoxidation of benzyl alcohol. H2-treated Cu0.18Ru0.05CeOz showed a slightly larger initial conversion of benzyl alcohol than O2-treated Cu0.18Ru0.05CeOz, suggesting that the reduced structure of Cu0.18Ru0.05CeOz was active for the ammoxidation. The integration of both Cu and Ru resulted in the efficient promotion of ammoxidation, in which the Ru species were involved in the conversion of benzyl alcohol and Cu species were required for selective production of benzonitrile.

Enhanced low-temperature H2-selective catalytic reduction performance and selectivity of Pt/ZSM-5–TiO2 washcoated monolithic catalysts for NOx reduction

Hydrogen-selective catalytic reduction (H2-SCR) is a promising technology for reducing nitrogen oxide (NOx) emissions at low temperatures, but the selectivity of this process is limited by the generation of N2O. To achieve enhanced denitrification (deNOx) performance, H2-SCR catalysts with mixed zeolite and TiO2 supports washcoated on monolithic cordierite were developed. The catalyst support, active metal type and content, and monolithic cordierite cell density significantly influenced the H2-SCR performance. The xPt/TiO2 catalysts (where x is the metal content, wt.%) achieved >90% NOx conversion 135–180 °C, whereas the xPd/TiO2 catalysts exhibited poor H2-SCR activity, with <30% NOx conversion. In contrast to 0.5Pt/TiO2, the 0.5Pt/zeolite catalysts achieved high NOx conversion at 140–150 °C (91% at 140 °C for 0.5Pt/ZSM-5 > 89% at 140 °C for 0.5Pt/BETA >85% at 150 °C for 0.5Pt/SSZ-13), suggesting that zeolite supports significantly promote H2-SCR activity at low reaction temperatures. For the 0.5Pt/ZSM-5 washcoated monolithic catalyst, increasing the cell density from 400 to 900 cpsi significantly improved the NOx conversion from 52% to 90% at 100 °C owing to the increased geometric surface area and open frontal area of monolithic cordierite. For catalyst with mixed supports (0.5Pt/yZSM-5zTiO2) changing the ZSM-5/TiO2 ratio (y:z) from 25:75 to 90:10 increased the low-temperature NOx conversion from 39% to 89% at 100 °C, indicating that the deNOx characteristics can be tuned. With NO as the reactant, the 0.5Pt/90Z10T catalyst produced the lowest N2O share (8–17%) within the temperature window of maximum NOx conversion, resulting in an increased N2 share (83–88%). Thus, the synergetic effect of mixed ZSM-5/TiO2 catalyst supports can enhance low-temperature NOx conversion and mitigate N2O formation.

A highly efficient Ni/3DOM-La2O2CO3 catalyst with ordered macroporous structure for CO2 methanation

The global focus on new energy sources and energy storage methods has prompted significant research interest. Ni-based catalysts for CO2 methanation have the potential for industrialization, but face challenges such as high-temperature sintering, carbon deposition, and unstable catalytic activity; of which similar problems exist in NH3 decomposition reactions. A 10%Ni/3DOM-La2O2CO3 catalyst, featuring a three-dimensional ordered macroporous (3DOM) structure, demonstrated competitive low-temperature catalytic performance in CO2 methanation through formate intermediates. Comprehensive characterizations revealed improved Ni dispersion and carbon deposition prevention due to the 3DOM structure, enhancing catalytic activity. This structural advantage also translated to improved performance in ammonia decomposition.

Experimental and numerical study of Cu-SSZ-13 SCR system for NOx reduction and hydrothermal aging under diesel exhaust conditions

Selective catalytic reduction (SCR) is a crucial technique for mitigating nitrogen oxides emission of internal combustion engines. Compared with vanadium-based catalysts, copper-based molecular sieve catalysts exhibit superior low-temperature catalytic performance and anti-aging properties. The catalytic characteristics of Cu-SSZ-13 catalyst in both fresh and aged states are investigated through experimental and numerical simulations. The catalytic performance of Cu-SSZ-13 catalyst with 200 g/L coating is investigated under wide inlet temperatures (180 °C–450 °C) and ANR (ammonia to nitrogen ratio) (1–1.4) conditions via an engine emission test device. Further, the apparatus is adopted to evaluate performance at various aging temperatures (600 °C, 700 °C, and 800 °C). The aging factor is introduced based on experimental results to establish and correct the kinetic model for SCR aging state. The results illuminate that the increase of ANR fails to compensate for decline of catalytic efficiency under low-temperature conditions (150 °C).The generated quantity of isocyanate acid through the side reaction of urea hydrolysis increases proportionally with ANR. And it increased supply only resulted in a marginal 1 %–3 % improvement of catalytic efficiency. As SV decreases from 60,000 h−1 to 35,000 h−1, the catalyst efficiency increases from 22 % to 45 %, resulting in an elevation of reactant concentration and its gradient on the catalyst surface. This leads to accelerated reaction rates and enhanced diffusion effects. The catalytic efficiency can be significantly enhanced at low temperatures when NO2 fraction in NOx falls within the range of 10 %–25 %. The sensitivity of SCR reactions to aging varies at low temperatures (<250 °C) due to the distinct reaction sites on catalyst for different types of SCR reactions. The NO2 SCR reactions exhibit minimal susceptibility, while the rapid SCR reactions are significantly impeded. Moreover, it has been observed that the catalyst microstructure was completely deteriorated under hydrothermal aging test at 900 °C operating condition. In general, the low-temperature catalytic performance of Cu-SSZ-13 catalyst can be further optimized by pretreating inlet gas components and optimizing the catalyst structure.

Insights into the underpinning effect of graphene in Cu1Mn10 on enhancing the low-temperature catalytic activity for CO oxidation

CO emission is a critical issue of industrial processes such as steel-smelting, cement manufacturing, and waste incineration. Catalytic oxidation based on Cu–Mn binary catalysts shows great potential for efficient removal of CO, whereas their practical applicability is limited by the inferior low-temperature catalytic activity and the high catalyst cost owing to a substantial quantity of Cu. In this study, doping graphene is designed to adjust the electron transfer capability to improve the low-temperature catalytic activity as well as reduce the amount of Cu, and thereby Cu1Mn10 catalysts doped with slight amounts of graphene (x%G-Cu1Mn10, x is 1∼5) were fabricated. It was found that the introduction of graphene could form effective electron transport channels to enhance the intermetallic interaction and oxygen vacancy generation, thus improving the low-temperature catalytic performance of the Cu1Mn10 catalyst. Among all the catalysts, 4%G-Cu1Mn10 exhibited the highest activity, achieving CO conversion of 92% at 110 °C at a weight hourly space velocity of 120,000 mL/(g∙h). The introduction of graphene also enabled the catalyst with excellent catalytic activity and stability at a relative humidity of 70%. Attractively, 4%G-Cu1Mn10 can be further loaded into the polyester fabric, presenting great application potentials in the effective elimination of CO during the dust removal process since the flue gas temperature in the dust collector is just around the T90% and the catalyst that is inside of fabric fiber rather than on the fabric surface can be rarely influenced by the dust. In general, doping graphene provides a facile method to enhance the low-temperature activities of the Cu–Mn binary catalysts and cut down the use of valuable Cu, showing great application potential.

Excellent low-temperature activity for oxidation of benzene serials VOCs over hollow Pt/CoMn2O4 sub-nanosphere: Synergistic effect between Pt and CoMn2O4 on improving oxygen activation

Constructing the interfacial active sites between noble metals and oxides is an effective way to enhancing the catalytic performance of noble metal-supported catalysts. Meanwhile, ultra-low dosage of the noble metal Pt but obtaining favorable catalytic activity is still major challenge to prepare noble metal-supported catalysts. Herein, the active Pt-CoMn2O4 interface with strong metal-support interaction (SMSI) is designed by loading ultra-low Pt content (0.12 wt%) on hollow structured CoMn2O4 sub-nanosphere (Pt/CoMn2O4). Compared with the reference MnOx, CoMn2O4 and Pt/MnOx, Pt/CoMn2O4 shows excellent catalytic activity even in presence of H2O, which is capable of completely converting toluene, ethylbenzene and o-xylene at 163, 207 and 218 °C, respectively. Various characterizations and density functional theory (DFT) calculations are performed to reveal the role of CoMn2O4 and specify the synergistic effect between Pt and CoMn2O4 on surface properties and catalytic performance. Intriguingly, in situ-designed temperature-programmed techniques and in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy clarify the substitution of Co in CoMn2O4 enhances oxygen mobility, and the interface of Pt and support is the active sites for gaseous oxygen activation can also be confirmed by DFT calculation results. This SMSI is prone to promote the supplement of active oxygen species that is essential for excellent low-temperature catalytic oxidation performance. This study provides a new insight into the design of high-performance noble metal catalysts, and the understanding of textural structure, active species, synergistic effect, and mechanisms of catalytic systems.

Pr-modified vanadia-based catalyst for simultaneous elimination of NOx and chlorobenzene

The V2O5/TiO2 catalyst is the most concerned NH3-SCR catalytic system for simultaneous removal of NOx and chlorinated volatile organic compounds (Cl-VOCs). There is an urgent need to develop a vanadia-based catalyst with low vanadium loading and excellent low-temperature catalytic performance. In this work, the Pr and W co-doped vanadia-based catalysts were prepared by a simple impregnation method. After the doping of Pr and W, the vanadia-based catalyst exhibited the excellent catalytic activity for NOx reduction and chlorobenzene (CB) oxidation. The more abundant polymeric vanadyl species and crystalline V2O5 were observed on the PrV5W/Ti catalyst, which are contributing to NH3-SCR and CB oxidation activity. The redox capability and the amount of surface-active adsorbed oxygen of vanadia-based catalyst were improved markedly, thus promoting NH3-SCR and CB oxidation reaction on PrV5W/Ti. This catalyst is promising to be used in the muti-pollutant control reaction of NOx and VOCs.

Low-temperature catalytic performance improvement of Ru/TiO2{001} for o-dichlorobenzene oxidation

Chlorinated aromatics hydrocarbons were harmful to ecology and human health, whose catalytic combustion encounters problem of catalyst deactivation by chlorine poisoning. To simultaneously improve the catalytic activity, CO2 selectivity and stability of catalyst, the present study used the loading of Ru active component on the anatase TiO2 which preferentially exposes highly active {001} crystalline facets. Take o-dichlorobenzene (o-DCB) oxidation as a surrogate reaction, Ru/TiO2{001} showed lower T90% (temperatures with 90% conversion), higher CO2 selectivity and better stability than Pt/TiO2{001}, Pd/TiO2{001} and Ru/commercial TiO2 (Ru/TiO2-C). The excellent results could be attributed to the strong metal support interaction between Ru species and TiO2{001}, with more oxygen vacancies and higher surface oxygen concentration, more Lewis acid sites, enhanced low-temperature reducibility, more surface Ti3+ species, more surface Ru4+ species, and highly dispersed Ru species, favoring the excellent low temperature catalytic activity and CO2 selectivity of Ru/TiO2{001}. In addition, the less Cl species on the used 1.5% Ru/TiO2{001} indicated their effectively removal, which is the core issue for the deep oxidation of o-DCB. Furthermore, the in situ FTIR spectroscopy gave the detail oxidation route of o-DCB over 1.5% Ru/TiO2{001}, that the co-adsorption of o-DCB and O2 on Ru/TiO2{001} surface were calculated based on the density functional theory calculations. The present study gave a new insight into the new pathway for the design of promising catalysts for the treatment of CAHs.

Unraveling the synergy between MnOx and CeO2 in MnOx-CeO2 SCR catalysts based on experimental and DFT studies

MnOx-CeO2 catalysts have shown great potential as selective catalytic reduction of NOx by NH3 (NH3-SCR) at temperature below 300 °C. While the improved catalytic activity due to the synergy between MnOx and CeO2 in MnOx-CeO2 catalysts is widely acknowledged, the synergistic mechanism in NH3-SCR reaction remains elusive due to the lack of direct evidences. In this study, we report a comprehensive study of how MnOx and CeO2 interacted during NH3-SCR in two designed MnOx-CeO2 catalysts with different Ce4+ concentration through both experimental and theoretical approaches. Our results reveal that electron transfer from Mn2+ to Ce4+ induced the formation of surface oxygen vacancy on the CeO2, leading to the synergistic promotion of low-temperature catalytic performance by establishing Mn-redox and Ce-redox cycles to activate NH3 and O2, respectively. This work provides a distinct mechanism diagram of the synergy between MnOx and CeO2, which sheds light on the rational design of low-temperature NH3-SCR catalysts.

Oxygen vacancy-engineered in ethylene glycol solvated α-MnO2 for low temperature catalytic oxidation of toluene

Synthesis of catalyst by the organic solvent is an attractive strategy for improving the oxygen vacancy concentration and catalytic activity. Due to the excellent reducibility of ethylene glycol (EG), the reduction strategy was designed to synthesize α-MnO2-EG, and for toluene oxidation. The results showed that EG could significantly increase the oxygen vacancy concentration and catalytic activity of α-MnO2-EG. The oxygen vacancy concentration of α-MnO2-EG-160 is 30% higher than that of α-MnO2-H2O, which leads to the significant low-temperature catalytic performance of the α-MnO2-EG-160 catalyst (T90 = 183 °C), much lower than the currently reported MnO2-based catalysts. The structure–activity relationship of the α-MnO2-EG-160 has been explained. To be specific, EG macromolecules could intrude into [MnO6] framework to exfoliate oxygen atoms and generate oxygen vacancies, which not only improves redox properties, but also promotes the adsorption of toluene. Furthermore, the toluene catalytic mechanism of α-MnO2-EG-160 based on oxygen vacancies was proposed.

Engineering the Quaternary Hydrotalcite-Derived Ce-Promoted Ni-Based Catalysts for Enhanced Low-Temperature CO2 Hydrogenation into Methane.

Ce-promoted NiMgAl mixed-oxide (NiCex-C, x = 0, 1, 5, 10) catalysts were prepared from the quaternary hydrotalcite precursors for CO2 hydrogenation to methane. By engineering the Ce contents, NiCe5-C showed its prior catalytic performance in low-temperature CO2 hydrogenation, being about three times higher than that of the Ce-free NiCe0-C catalyst (turnover frequency of NiCe5-C and NiCe0-C: 11.9 h-1 vs. 3.9 h-1 @ 225 °C). With extensive characterization, it was found that Ce dopants promoted the reduction of NiO by adjusting the interaction between Ni and Mg(Ce)AlOx support. The highest ratio of surface Ni0/(Ni2+ + Ni0) was obtained over NiCe5-C. Meanwhile, the surface basicity was tailored with Ce dopants. The strongest medium-strength basicity and highest capacity of CO2 adsorption was achieved on NiCe5-C with 5 wt.% Ce content. The TOF tests indicated a good correlation with medium-strength basicity over the NiCex-C samples. The results showed that the high medium-strength and Ce-promoted surface Ni0 species endows the enhanced low-temperature catalytic performance in CO2 hydrogenation to methane.

New insights into the relationship between Cu–Ce interaction and reactive Cu species in CuOx-CeO2 catalysts for preferential oxidation of carbon monoxide in excess hydrogen

A group of CuOx-CeO2 catalysts for preferential oxidation of carbon monoxide (CO-PROX) is designed by constructing different distribution status of Cu species on similar CeO2 support to adjust the Cu–Ce interaction strength. Cycled temperature programmed reduction by hydrogen (H2-TPR) indicates the strength of Cu–Ce interaction can impact the amount and redox properties of surface highly dispersed CuOx and strongly bonded Cu-[Ox]-Ce species, which respectively determines the catalytic performance at low and high temperature. Temperature programed desorption of H2 (H2-TPD) reveals the presence of large amounts of Cu-[Ox]-Ce species can inhibit H2 adsorption and dissociation, which increases the O2 selectivity toward CO oxidation. Moreover, temperature programmed desorption of CO2 (CO2-TPD) and in situ diffuse reflectance infrared Fourier transform spectra (DRIFTs) illustrates that H2O and CO2 influences the low-temperature catalytic performance mainly by competitive adsorption with CO on surface highly dispersed reactive Cu+ sites. This work aims to shed light on the underlying Cu–Ce interaction regime, and guide the design of high-performance CuO–CeO2 catalysts in realistic reaction conditions.

Engineering Surface Properties of CuO/Ce0.6Zr0.4O2 Catalysts for Efficient Low-Temperature Toluene Oxidation

The development of superior low-temperature catalytic performance and inexpensive catalysts for the removal of volatile organic compounds (VOCs) is crucial for their industrial application. Herein, CuO/Ce0.6Zr0.4O2 catalysts calcinated at different temperatures (Cu/CZ-X, X represented calcination temperature) were prepared and used to eliminate toluene. It can be found that Cu/CZ-550 presented the highest low-temperature catalytic activity, with the lowest temperature (220 °C) 50% conversion of toluene, the highest normalized reaction rate (3.1 × 10−5 mol·g−1·s−1 at 180 °C) and the lowest apparent activation energy value (86.3 ± 4.7 kJ·mol−1). Systematically, the surface properties analysis results showed that the optimum redox property, abundant oxygen vacancies, and plentiful surface Ce3+ species over Cu/CZ-550 were associated with the strong interaction between Cu and support could significantly favor the adsorption and activation of toluene, thus resulting in its superior catalytic performance.