Activity For Low-temperature Oxidation Research Articles

Enhanced Catalytic Oxidation Reactivity over Atomically Dispersed Pt/CeO2 Catalysts by CO Activation.

The elevation of the low-temperature oxidation activity for Pt/CeO2 catalysts is challenging to meet the increasingly stringent requirements for effectively eliminating carbon monoxide (CO) from automobile exhaust. Although reducing activation is a facile strategy for boosting reactivity, past research has mainly concentrated on applying H2 as the reductant, ignoring the reduction capabilities of CO itself, a prevalent component of automobile exhaust. Herein, atomically dispersed Pt/CeO2 was fabricated and activated by CO, which could lower the 90% conversion temperature (T90) by 256 °C and achieve a 20-fold higher CO consumption rate at 200 °C. The activated Pt/CeO2 catalysts showed exceptional catalytic oxidation activity and robust hydrothermal stability under the simulated working conditions for gasoline or diesel exhausts. Characterization results illustrated that the CO activation triggered the formation of a large portion of Pt0 terrace sites, acting as inherent active sites for CO oxidation. Besides, CO activation weakened the Pt-O-Ce bond strength to generate a surface oxygen vacancy (Vo). It served as the oxygen reservoir to store the dissociated oxygen and convert it into active dioxygen intermediates. Conversely, H2 activation failed to stimulate Vo, but triggered a deactivating transformation of the Pt nanocluster into inactive PtxOy in the presence of oxygen. The present work offers coherent insight into the upsurging effect of CO activation on Pt/CeO2, aiming to set up a valuable avenue in elevating the efficiency of eliminating CO, C3H6, and NH3 from automobile exhaust.

The Surface/Interface Modulation of Platinum Group Metal (PGM)-Free Catalysts for VOCs and CO Catalytic Oxidation.

Effective management of volatile organic compounds (VOCs) and carbon monoxide (CO) is critical to human health and the ecological environment. Catalytic oxidation is one of the most promising technologies for achieving efficient VOCs and CO emission control. Platinum group metal (PGM)-free catalysts are recently receiving sustainable attention in catalyzing VOCs and CO removal due to their low cost, superior catalytic activity, and excellent stability, but PGM-free catalysts face challenges in low-temperature catalytic efficiency. In this mini-review, starting with discussing the catalytic mechanism of VOCs and CO oxidation, we summarize the surface/interface modulation strategies of PGM-free catalysts to promote oxygen and VOCs/CO molecule activation for enhanced low-temperature oxidation activity, including oxygen vacancy engineering, heteroatom doping, surface acidity modification, and active interface construction. We highlight the currently remaining challenges and prospects of advanced PGM-free catalyst development for highly efficient VOCs and CO emission control in practical applications.

Platinum on High-Entropy Aluminate Spinels as Thermally Stable CO Oxidation Catalysts

Thermal degradation is a leading cause of automotive catalyst deactivation. Because high-entropy oxides are uniquely stabilized at high temperatures via an increase in configurational entropy, these materials may offer new mechanisms for preventing the thermal deactivation of precious metal catalysts. In this work, we evaluated platinum loaded on simple and high-entropy aluminate spinels (MAl2O4, where M = Co, Cu, Mg, Ni, or mixtures thereof) in carbon monoxide oxidation before and after aging at 800 °C. Pt supported on all simple spinels showed significant deactivation after thermal aging compared to the fresh samples, with T90 increasing by at least 60 °C. However, Pt on high-entropy spinels had nearly the same or better activity after aging, with T90 increasing by only 6 °C at most. During aging and reduction, copper exsolved from the spinel supports and alloyed with platinum. This interaction promoted low temperature oxidation activity, presumably through weakened CO binding, but did not prevent deactivation. On the other hand, Co, Mg, and Ni constituents promoted stronger CO bonding, as evidenced by apparent negative order kinetics and poor activity at low temperatures. High-entropy spinels, containing a variety of active metals, displayed synergetic reactant adsorption capacity and cooperative effects with supported platinum particles, which collectively prevented thermal deactivation.

Relationship between low-temperature oxidation activity and second-stage ignition delay: Experimental insights on n-pentanol / hydrogenated catalytic biodiesel blends

N-pentanol exhibits promising potential as a sustainable and eco-friendly biomass energy source. However, certain challenges such as ignition difficulty and unstable combustion exist. This study investigates the influence of low-temperature auto-ignition of n-pentanol/HCB (Hydrogenated Catalytic Biodiesel) blends on ignition and combustion characteristics and evaluates the correlation between low-temperature oxidation and second-stage ignition delay. Results show a linear positive correlation between the HCB content in n-pentanol and its low-temperature oxidation reactivity. The stronger the low-temperature oxidation activity of the blends, the shorter the second-stage ignition delay of blends. When the HCB content in blends is below 40 %, the low-temperature oxidation rate initially increases and then decreases. However, the low-temperature oxidation rate increases again when the HCB content exceeds 40 %. Moreover, the relationship between the initial CO2 generation rate and the HCB blending ratio follows an Exp exponential function under different critical compression ratios. Beyond 43.7 % HCB, an acceleration in the high-temperature combustion rate owing to an increase in the low-temperature oxidation rate again. In addition, the minimum ignition limit of n-pentanol/HCB blends was identified with 40 % HCB blends closely resembling diesel conditions and 50 % HCB blends showing a lower ignition limit, characterized by a critical temperature and pressure of 517.3 K and 8.66 bar, respectively. Furthermore, two distinct conditions for the minimum ignition boundary region of n-pentanol/HCB blends were defined, offering practical insights. In summary, a blend with a 50 % HCB ratio provides a promising solution for the low-temperature ignition and stable combustion of n-pentanol, addressing the challenges of simultaneous use in internal combustion engines.

Significant Enhanced SO2 Resistance of Pt/SiO2 Catalysts by Building the Ultrathin Metal Oxide Shell for Benzene Catalytic Combustion.

A noble metal catalyst shows excellent low-temperature oxidation activity in the catalytic combustion of benzene but has the problem of SO2 poisoning. We all know that SO2 easily competes with the reactant molecules for adsorption of the active site and has electronic effects on the active site to deactivate the catalyst. Therefore, the sulfur resistance of catalysts is the key problem to be solved in the process of catalytic combustion of benzene. Herein, the Pt/SiO2 catalyst with an ordered mesoporous structure was prepared by a one-step hydrothermal method, and MgO, ZnO, and MnOx were, respectively, coated on the surface of Pt/SiO2 as ultrathin shells to improve the sulfur resistance of Pt/SiO2. We observed that the sulfur resistance of the Pt/SiO2 catalyst was significantly improved due to the protective effect of the metal oxide shell. By comparing the three core-shell catalysts, it was found that the Pt/SiO2@MnOx catalyst coated with a MnOx shell had the best performance. The reason was that the MnOx shell not only protected the Pt active site but also had a good electron transfer effect on the core Pt, so it could effectively avoid the rapid adsorption poisoning of SO2 on the active Pt0 site. In addition, it was verified that the excellent redispersion of MnOx species in a SO2 atmosphere could increase the low-temperature oxidation activity of the Pt/SiO2@MnOx catalyst. Meanwhile, in situ DRIFT results also confirmed that the MnOx shell could significantly promote the oxidation of benzene molecules in the SO2 atmosphere.

Spontaneous Combustion Characteristics and Inhibition of Air-Dried Coal with Varying Water Soaking Times

ABSTRACT Coal left in the goaf is prone to oxidation reactions when soaked in water and air-dried, which can cause a temperature increase and potentially lead to a mine fire. The spontaneous combustion characteristics of residual coal soaked in the goaf differ significantly from those of dry coal. Analyzing the variation rules of functional groups in coals with different water soaking times (WSTs) during low-temperature oxidation and exploring the inhibitory effect of an inhibitor on coals with different WSTs are vital in preventing and controlling fires in soaked and air-dried coal seams in the goaf. This paper analyzes the variation rules of functional groups in raw coal samples and samples soaked for one, three, and five months, as well as the corresponding samples under the influence of the inhibitor, MgCl2, using an experimental system of coal low-temperature oxidation and a Fourier transform infrared spectrometer. The following findings were obtained: as the WST increases, the aliphatic hydrocarbon content increases, the low-temperature oxidation activity becomes higher, and the inhibition effect of the inhibitor weakens gradually. As the WST increases, the -CH2, -CH3, -OH, and -COOH contents fall gradually, while the C=O content rises. At the beginning of the oxidation temperature rise (30–70°C), the inhibitor, MgCl2, slows down the consumption of oxygen-containing functional groups and aliphatic hydrocarbon functional groups. However, when the temperature exceeds 130°C, its inhibitory effect on coal oxidation weakens gradually. In this case, a growing number of functional groups are involved in coal oxidation, and the inhibitor fails to effectively prevent coal oxidation. Therefore, it is necessary to strengthen temperature monitoring in the goaf and regularly replenish inhibitors in soaked and air-dried coal seams to enhance the inhibitory effect and prevent the SC of such seams.

A quantum chemical computation and model investigation for autoignition kinetic of a long chain oxygenate: Tri-propylene glycol methyl ether

Tri-propylene glycol methyl ether (TPGME) is a promising bio-based oxygenated fuel for advanced engines. The internal H-migration of peroxy (ROO) radicals is a critical factor in the process of TPGME autoignition. In this work, the potential energy surfaces (PESs) of the internal H-migration of ROO radicals as well as alcohol elimination of TPGME were calculated with a high-level DLPNO-CCSD(T)/cc-pVTZ//B3LYP-D3/6–311++G(d,p) method. Rate constants for target reactions were then obtained over a temperature range of 300–1000 K using conventional transition state (CTST) theory. The rate constants for above reactions in the Burke’s model [Combust. Flame. 2015, 16 2(7), 2916–2927] were updated with the calculated results, followed by the modification for important reaction using an analogy strategy, to obtain a revised model. It was found that the feasibility of the H-migration of ROO radicals depended on the transition state ring size and the C-H bond energy of the transferred hydrogen atom, with 1, 5H-migration and 1, 6H-migration played a leading role in the process of TPGME autoignition. Validation against the shock tube (ST), jet stirred reactor (JSR) and collaborative fuel research (CFR) engine measurements from the literature showed that the revised model improved the prediction accuracy. In comparison to n-heptane, the CFR simulation proved that more available hydrogens of 1,5H-migration and 1,6H-migration, as well as higher concentrations and rate of production (ROP) for key low-temperature intermediate species, were contributing factors that stronger low-temperature oxidation activity of TPGME.

Preparation of porous MnO2/CeO2 composite for the effective removal of formaldehyde from air

A porous MnO2/CeO2 composite catalyst was prepared via the template method for the catalytic decomposition of formaldehyde (HCHO). The physical and chemical properties of the catalysts were intensively characterized via X-ray diffraction, transmission electron microscopy, Brunauer-Emmett-Teller analysis, temperature programmed reduction system and X-ray photoelectron spectroscopy. The catalytic activity and stability for HCHO oxidation were measured via a fixed bed reactor, and the effects of physical and chemical properties of the catalysts on their catalytic performance were investigated. The results showed that the porous MnO2/CeO2 catalyst had abundant 3D pore structures, a large specific surface area, an amorphous structure, and an abundance of lattice oxygen species. Thus, the MnO2/CeO2 catalyst had high catalytic activity and stability for HCHO decomposition. This catalyst completely decomposed HCHO at 90 °C and maintained a 99% HCHO conversion rate over 72 h. The highly porous structure reduced the diffusion resistance in the reaction process and improved the efficiency of catalytic decomposition of HCHO. Doping with CeO2 improved the low temperature oxidation activity and catalytic stability of the porous MnO2/CeO2 catalyst. The porous MnO2/CeO2 composite was an effective agent for the removal of harmful HCHO from the air.

Influence of Co-Precipitation Agent on the Structure, Texture and Catalytic Activity of Au-CeO2 Catalysts in Low-Temperature Oxidation of Benzyl Alcohol

The aim of the study was to establish the influence of a co-precipitation agent (i.e., NaOH–immediate precipitation; hexamethylenetetramine/urea–gradual precipitation and growth of nanostructures) on the properties and catalytic activity of as-synthesized Au-CeO2 nanocomposites. All catalysts were fully characterized with the use of XRD, nitrogen physisorption, ICP-OES, SEM, HR-TEM, UV-vis, XPS, and tested in low-temperature oxidation of benzyl alcohol as a model oxidation reaction. The results obtained in this study indicated that the type of co-precipitation agent has a significant impact on the growth of gold species. Immediate co-precipitation of Au-CeO2 nanostructures with the use of NaOH allowed obtainment of considerably smaller and more homogeneous in size gold nanoparticles than those formed by gradual co-precipitation and growth of Au-CeO2 nanostructures in the presence of hexamethylenetetramine or urea. In the catalytic tests, it was established that the key factor promoting high activity in low-temperature oxidation of benzyl alcohol was size of gold nanoparticles. The highest conversion of the alcohol was observed for the catalyst containing the smallest Au particle size (i.e., Au-CeO2 nanocomposite prepared with the use of NaOH as a co-precipitation agent).

MnO2-decorated N-doped carbon nanotube with boosted activity for low-temperature oxidation of formaldehyde

Low-temperature oxidative degradation of formaldehyde (HCHO) using non-noble metal catalysts is challenging. Herein, novel manganese dioxide (MnO2)/N-doped carbon nanotubes (NCNT) composites were prepared with varying MnO2 content. The surface properties and morphologies were analyzed using X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and transmission electron microscope (TEM). Comparing with MnO2/carbon nanotubes (CNTs) catalyst, the 40% MnO2/NCNT exhibited much better activity and selectivity for HCHO oxidation, mineralizing 95% of HCHO (at 100 ppm) into CO2 at 30 °C at a gas hourly space velocity (GHSV) of 30,000 mL h-1 g-1. Density functional theory (DFT) calculation was used to analyze the difference in the catalytic activity of MnO2 with CNTs and NCNT carrier. It was confirmed that the oxygen on NCNT was more active than CNTs, which facilitated the regeneration of MnO2. This resulted in remarkably boosted activity for HCHO oxidation. The present work thus exploited an inexpensive approach to enhance the catalytic activity of transition metal oxides via depositing them on a suitable support.

Study on Oxidation Activity of CuCeZrOx Doped with K for Diesel Engine Particles in NO/O2

CuCeZrOx and KCuCeZrOx catalysts were synthesized and coated on the blank diesel particulate filter (DPF) substrate and a particulate matter (PM) loading apparatus was used for soot loading. The catalytic performances of soot oxidation were evaluated by temperature programmed combustion (TPC) test and characterization tests were conducted to investigate the physicochemical properties of the catalysts. The reaction mechanism in the oxidation process was analyzed with diffuse reflectance infrared Fourier transform spectroscopy. The results demonstrated that CuCeZrOx catalyst exhibited high activities of soot oxidation at low temperature and the best results have been attained with Cu0.9Ce0.05Zr0.05Ox over which the maximum soot oxidation rate decreased to 410 °C. Characterization tests have shown that catalysts containing 90% Cu have uniformly distributed grains and small particle sizes, which provide excellent oxidation activity by providing more active sites and forming a good bond between the catalyst and the soot. The low-temperature oxidation activity of soot could be further optimized due to the excellent elevated NO’s conversion rate by partially substituting Cu with K. The maximum particle oxidation rate can be easily realized at such a low temperature as 347°C.

Roles of oxygen vacancy and Ox− in oxidation reactions over CeO2 and Ag/CeO2 nanorod model catalysts

Though the catalytic oxidation of CO, NO and soot over CeO2 could be understood within a similar Mars-van Krevelen-type mechanism, these reactions were likely to be driven by different active phases. In this work, several CeO2 and Ag/CeO2 nanorods with different contents of surface oxygen vacancies (VO-s) and active oxygen species (Ox−) were designed as model catalysts. Their catalytic performance indicated that, CO oxidation was determined by pre-existing ceria VO-s, while Ox− participated in NO and soot oxidation directly. Besides, by loading silver onto the high-temperature aged CeO2 nanorods, Ag/CeO2 catalysts with high availability of ceria lattice oxygen were obtained, whose low-temperature oxidation activity was proven comparable to that of the platinum catalysts. In this sense, the model designing in this work not only provided methods to find out proper reactivity descriptors, but also conferred low-cost catalysts with high practical potential.

Fully Dispersed Rh Ensemble Catalyst To Enhance Low-Temperature Activity.

Minimizing the use of precious metal catalysts is important in many applications. Single-atom catalysts (SACs) have received much attention because all of the metal atoms can be used for surface reactions. However, SACs cannot catalyze some important reactions that require ensemble sites. Here, Rh catalysts were prepared by treating 2 wt % Rh/CeO2 hydrothermally at 750 °C for 25 h. Nearly 100% dispersion was obtained, but the surface Rh atoms were not isolated (denoted as ENS). They catalyzed the oxidation of C3H6 or C3H8 at low temperatures, but these oxidations did not occur on the Rh SAC. When the simultaneous oxidation of CO, C3H6, and C3H8 was performed, the T20 (temperature at conversion 20%) for CO oxidation increased significantly from 40 °C for sole CO oxidation to 180 °C on SAC due to the competitive adsorption of hydrocarbons. However, T20 increased much less on ENS, from 60 to 100 °C. ENS exhibited superior activity for low-temperature oxidation. During hydrothermal treatment for 25 h, the Rh size initially increased from 2.3 to 6.7 nm then decreased to 0.9 nm. The surface hydroxyl groups formed on the catalyst surface help detach Rh atoms from Rh clusters, while preventing the reaggregation of dispersed Rh atoms into Rh clusters. This fully dispersed catalyst would have maximum atom-efficiency while catalyzing various surface reactions.

Advances on transition metal oxides catalysts for formaldehyde oxidation: A review

ABSTRACT This article highlights recent advances in the development of transition metal-based catalysts for formaldehyde oxidation, particularly the enhancement of their catalytic activity for low-temperature oxidation. Various factors that enhance low-temperature activity are reviewed, such as morphology and tunnel structures, synthesis methods, specific surface area, amount and type of active surface oxygen species, oxidation state, and density of active sites are discussed. In addition, catalyst immobilization for practical air purification, reaction mechanism of formaldehyde oxidation, and the reaction parameters affecting the overall efficiency of the reaction are also reviewed.

Sodium Rivals Silver as Single-Atom Active Centers for Catalyzing Abatement of Formaldehyde.

The development of efficient alkali-based catalysts for the abatement of formaldehyde (HCHO), a ubiquitous air pollutant, is economically desirable. Here we comparatively study the catalytic performance of two single-atom catalysts, Na1/HMO and Ag1/HMO (HMO = Hollandite manganese oxide), in the complete oxidation of HCHO at low temperatures, in which the products are only CO2 and H2O. These catalysts are synthesized by anchoring single sodium ions or silver atoms on HMO(001) surfaces. Synchrotron X-ray diffraction patterns with structural refinement together with transmission electron microscopy images demonstrate that single sodium ions on the HMO(001) surfaces of Na1/HMO have the same local structures as silver atoms of Ag1/HMO. Catalytic tests reveal that Na1/HMO has higher catalytic activity in low-temperature oxidation of HCHO than Ag1/HMO. X-ray photoelectron spectra and soft X-ray absorption spectra show that the surface lattice oxygen of Na1/HMO has a higher electronic density than that of Ag1/HMO, which is responsible for its higher catalytic efficiency in the oxidation of HCHO. This work could assist the rational design of cheap alkali metal catalysts for controlling the emissions of volatile organic compounds such as HCHO.

Understanding low temperature oxidation activity of nanoarray-based monolithic catalysts: from performance observation to structural and chemical insights

Monolithic catalysts have been widely used in automotive, chemical, and energy relevant industries. Nanoarray-based monolithic catalysts have been developed, demonstrating high catalyst utilization efficiency and good thermal/mechanical robustness. Compared with the conventional washcoat-based monolithic catalysts, they have shown advances in precise and optimum microstructure control and feasibility in correlating materials structure with properties. Recently, the nanoarray-based monolithic catalysts have been studied for low temperature oxidation of automotive engine exhaust and exhibited interesting and promising catalytic activities. This review focuses on discussing the key structural parameters of nanoarray catalyst that affect the catalytic performance from the following aspects: (1) geometric shape and crystal planes, (2) guest atom doping and defects, (3) array size and size-assisted active species loading, and (4) the synergy effect of metal oxide in composite nanoarrays. Prior to the discussion, an overview of the current status of synthesis and development of the nanoarray-based monolithic catalysts is introduced. The performance of these materials in low temperature simulated engine exhaust oxidation is also demonstrated. We hope this review will elucidate the science and chemistry behind the good oxidation performance of the nanoarray-based monolithic catalysts and serve as a timely and useful research guide for rational design and further improvement of the nanoarray-based monolithic catalysts for automobile emission control.

Synergetic effect of Pd addition on catalytic behavior of monolithic platinum–manganese–alumina catalysts for diesel vehicle emission control

The advanced diesel emission control catalyst Pt–Pd–MnOx–Al2O3 has been developed on the basis of the synergetic effect of Pt with Pd and manganese oxides observed in hydrocarbon and carbon monoxide oxidation reactions. This effect allows a decrease in the total loadings of Pt and Pd down to 0.52g/L in the monolithic catalyst, providing high activity in low temperature oxidation of light hydrocarbons and high thermal stability.The catalytic activity of Pt–Pd–MnOx–Al2O3 monolithic catalysts in butane oxidation and DIESEL tests depends on the Pt and Pd precursors, their individual loadings and their ratio (Pt/Pd). For a selected Pt precursor at its content 0.17g/L, the catalytic performance of Pt–Pd–MnOx–Al2O3 catalyst improves with an increase in Pd loading from 0 to 0.35g/L and is nearly constant at a higher Pd loading (0.70g/L). The most active monolithic Pt–Pd–MnOx–Al2O3 catalyst is prepared by using platinum-dinitrodiamine and palladium nitrate solutions as noble metal precursors.The catalytic activity in light hydrocarbon oxidation is shown to correlate with the RedOx properties of PdPt–MnOx–Al2O3 catalysts and the Pt–Pd particle size. The non-additive increase in the catalytic activity of bimetallic catalyst is suggested to connect with a formation of nanoscale PdO–PtOx particles on the surface of Mn3O4 and a modification of alumina structure by Mn3+ and PtPd clusters.

Effect of Ionic Liquids on Low-Temperature Oxidation of Coal

Three 1-butyl-3-methyl imidazolium ([BMIm]+) based ionic liquids (ILs) with different anions, including tetrafluoroborate ([BF4]−), acetate ([Ac]−), and trifluoromethane sulfonate ([OTf]−), were selected to investigate the inhibition effect of ILs on low-temperature oxidation of coal by oxidizing raw coal and ILs-treated coals under air during 20–180°C. The coal structure was characterized by Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). The Raman results show that the ILs treatment can inhibit the low-temperature oxidation activity of disorder structure in coal. The FTIR results demonstrate that the ILs can break and dissolve the associated hydrogen bonds and methylene groups, so that the low-temperature oxidation activity of ILs-treated coal is inhibited. The analysis on oxygen consumption and index gases of coals by gas chromatograph further confirms the spectra results that ILs treatment can inhibit the low-temperature oxidation of coal. The inhibition effect is in the order of [BMIm][OTf] > [BMIm][BF4] > [BMIm][Ac].

Copper-zinc oxide and ceria promoted copper-zinc oxide as highly active catalysts for low temperature oxidation of carbon monoxide

Copper-zinc oxide catalyst is prepared by co-precipitation technique. The effects of aging the precipitate in the parent solution and addition of CeO2 are investigated. CuO-ZnO catalyst containing 60% CuO and 40% ZnO is found to be active for the ambient temperature oxidation of CO; however the activity can be improved considerably by aging the catalyst during the precipitation process. Alternatively, the catalyst activity can be improved by the addition of CeO2 during the precipitation without aging the precipitate. A much higher CO oxidation activity is achieved for the CuO-ZnO catalyst system than that reported earlier for the same system. X-ray photoelectron spectra (XPS) and XRD results show that aging the catalyst during the precipitation process brings out more ZnO to the surface leading to higher CuO dispersion. This leads to the formation of relatively less crystalline or amorphous CuO that promotes the formation of more linear or weakly bonded CO on the catalyst surface as well as the creation of CuOx species under redox conditions. The metastable copper oxide species is a good electrophilic reagent with superior oxygen transfer capacity and the presence of weakly bonded surface CO ensures a low temperature oxidation activity for the catalyst. It is further seen that addition of ceria to the catalyst also brings out similar advantages. However, increase in the CeO2 content increases the CO bonding strength causing an increase in the light-off temperature (loss of low temperature oxidation activity), in spite of high overall reducibility and CO adsorption capacity of the catalyst. The reducibility and susceptibility to variation in the oxidation states of copper oxide are critical to the activity of the catalyst. It is also found that addition of CeO2 brings out a significant improvement in the catalyst stability over an extended reaction period as well as at elevated reaction temperature.

A novel mesoporous oxidation catalyst La-Co-Zr-O prepared by using nonionic and cationic surfactants as co-templates

The mesoporous La-Co-Zr-O catalyst with the atomic ratio of La + Co/La + Co + Zr = 0.5 was prepared by citric acid complexation-organic template decomposition method, using the mixture of nonionic p-octyl polyethylene glycol phenyl ether (OP) and cationic cetyltrimethyl-ammonium bromide (CTAB) as co-templates (LCZ-OP/CTAB-0.5). The results of BET and pore size distribution show that this sample possesses much bigger specific surface area (117.6 m 2/g) than those prepared by using single template CTAB (96.6 m 2/g, LCZ-CTAB) or by using conventional co-precipitation method (21.6 m 2/g, LCZ-CO). Both the samples obtained from single template CTAB and from the co-templates of OP and CTAB show very uniform mesoporous pore diameter (3.5–4.3 nm). The structural characterization results of XRD, XPS and Co K-edge EXAFS indicate that the highly dispersed Co 3O 4 crystallite should be the main active phase for CO oxidation. The crystal sizes of Co 3O 4 crystallites in LCZ-CTAB and LCZ-OP/CTAB-0.5 are 23.4 and 32.5 nm, respectively, which are much smaller than that in LCZ-CO (56.8 nm). The catalytic activity evaluation shows that the sample prepared by co-templates decomposition possesses much better activity for CO oxidation, especially the low temperature oxidation activity. However, the activity sequence of the samples is not the same as the crystal size of Co 3O 4 phase. On the contrary, the reducibility of bond Co–O and the reduced amount of Co 3O 4 phase below 500 °C for the samples are well correlated with their activity law, which should be a crucial factor for the oxidation performance of the samples.