Guisheng Wu

Effect of TiO2 crystal structure on the catalytic performance of Co3O4/TiO2 catalyst for low-temperature CO oxidation

Co3O4 catalysts supported on TiO2 with different crystalline structures (anatase (A), rutile (R) and P25 (Degussa)) were prepared by a deposition–precipitation method, and characterized by nitrogen adsorption/desorption, XRD, HR-TEM, EPR, Raman spectroscopy, XPS and H2-TPR techniques. The results show that Co3O4/TiO2 (A) exhibited the highest activity among the three Co3O4/TiO2 catalysts: CO can be completely oxidized to CO2 at −43 °C. When rutile TiO2 or P25 were used as the support, its catalytic activity was decreased obviously, because the TiO2 crystal structure has an influence on the physicochemical and catalytic properties of the Co3O4 catalysts. The results show that the Co3O4/TiO2 (A) catalyst contains Ti3+ species, which is in an unstable state and can affect the properties of Co3O4 by the interaction between the deposited Co3O4 and anatase TiO2 support. The Co3O4/TiO2 (A) catalyst exhibits highly defective structure and good oxygen adsorption ability. The reducibility of Co3O4 is improved by the anatase TiO2 support, resulting in Co3O4/TiO2 (A) possessing the better redox property than the other Co3O4/TiO2 catalysts, which is an important factor for its high catalytic activity.

Biodiesel synthesis over the CaO–ZrO2 solid base catalyst prepared by a urea–nitrate combustion method

CaO–ZrO2 solid base catalysts with Ca/Zr ratios varying from 4/6 to 9/1 were prepared via a urea–nitrate combustion method and used in the transesterification of soybean oil with methanol to produce biodiesel. The catalysts were characterized using N2 adsorption, XRD, SEM and CO2-TPD techniques, and tested for biodiesel synthesis. The results show that a new phase of CaZrO3 has been formed for the investigated CaO–ZrO2 catalysts. With the increase in Ca/Zr molar ratio, the total basic sites over the catalyst increase and a maximum is obtained over the CaO–ZrO2 catalyst with a Ca/Zr ratio of 8/2. A similar variation trend of biodiesel yield is observed, suggesting that the catalytic activity correlates well with the total basic sites on the catalyst surface. Furthermore, the turnover frequency (TOF) has been calculated for various CaO–ZrO2 catalysts and the result revealed that the catalytic activity also depends on the strength of basic sites. The urea–nitrate combustion method was demonstrated to be a simple, fast and effective method for the preparation of CaO–ZrO2 solid base catalysts, which could be effectively applied for biodiesel synthesis.

Promotional role of ceria on cobaltosic oxide catalyst for low-temperature CO oxidation

Ceria modified Co3O4 catalysts for low temperature CO oxidation were prepared by a precipitation–oxidation method, and characterized by low-temperature N2 adsorption/desorption, TPR, O2–TPD, CO–TPD and transient–response reaction. The roles of ceria in CeO2–Co3O4 catalyst and the effect of pretreatment on the performance of CeO2–Co3O4 for CO oxidation were investigated in detail. The results show that the presence of CeO2 can increase its surface area, reduce the crystal size of Co3O4, and improve obviously the catalytic activity and stability of Co3O4 for CO oxidation, such as its T100 is only −60 °C. It was also found that the addition of CeO2 can not only promote the adsorption of O2 and the reaction of adsorbed CO with surface oxygen species to form CO2, but also increase the CO2 desorption speed. The pretreatment method can affect the catalytic activity of CeO2–Co3O4, the catalyst treated in N2 exhibits higher catalytic activity for low-temperature CO oxidation due to formation of oxygen vacancy. The catalyst reduced in H2 shows lower activity for CO oxidation although it has more surface oxygen vacancies, because of the difficult desorption of CO2 on the reduced CeO2–Co3O4 catalyst.

The role of iron oxide in the highly effective Fe-modified Co3O4 catalyst for low-temperature CO oxidation

A series of iron modified cobalt oxide catalysts (FeaCobOx (b:a = MCo:MFe, 10 < x < 15)) were prepared by a co-precipitation method, characterized by nitrogen adsorption–desorption, XRD, Raman spectroscopy, XPS, H2-temperature programmed reduction, CO-temperature-programmed desorption, O2-temperature-programmed desorption and time-resolved CO titration, and their catalytic activities for CO oxidation were evaluated. When Co:Fe is 8:2 (mol), the Fe2Co8Ox catalyst exhibits a very high catalytic activity, in which CO can be completely converted to CO2 at −80 °C. The results show that the addition of Fe to Co3O4 can increase its surface area and inhibit the agglomeration of iron oxide, improve the reduction behaviour of Co3O4, optimize the ratio of Co3+:Co2+ on the catalyst surface, and promote CO adsorption and CO2 desorption on the catalyst surface. The oxygen species on Fe2Co8Ox are more active than those on Co3O4, and when the feed gas is lacking in oxygen the lattice oxygen of Fe2Co8Ox can easily overflow to the surface to participate in the oxidation of CO.

Effects of alkaline-earth oxides on the performance of a CuO–ZrO2 catalyst for methanol synthesis via CO2 hydrogenation

CuO–ZrO2 catalysts doped with alkaline-earth oxides were prepared by a urea-nitrate combustion method. The catalysts were characterized with N2 adsorption, N2O titration, XRD, H2-TPR, XPS and CO2-TPD techniques and tested for methanol synthesis from CO2 hydrogenation. With the incorporation of alkaline-earth oxides, the copper surface area increases remarkably, whereas the reducibility of CuO in the catalyst decreases. The doping of alkaline-earth oxides leads to an increase in the strength and contribution of the strong basic site on the catalyst surface. The results of catalytic tests indicate that the conversion of CO2 depends not only on the copper surface area but also on the reducibility of CuO in the catalyst, and the latter is a predominant factor for CaO-, SrO- and BaO-doped CuO–ZrO2 catalysts. The selectivity to methanol is related to the basicity of the catalyst. Moreover, the influence of the doping amount of MgO on the properties of CuO–ZrO2 was investigated, and the optimum catalytic activity is obtained as the amount of MgO doping is 5 mol%.

Effect of La2O3 on Catalytic Performance of Au/TiO2 for CO Oxidation

Abstract Pure TiO2 and La-doped TiO2 were prepared by the sol-gel method. Au was supported on TiO2 by the deposition-precipitation (DP) method, and its catalytic activity for CO oxidation was tested. The results showed that doping La in Au/TiO2 could improve its catalytic activity obviously for CO oxidation. The analyses of X-ray diffraction (XRD), temperature-programmed desorption (TPD), and Brunauer-Emmett-Teller (BET) surface area further showed that the presence of La in TiO2 not only increased its surface area and restrained the growth of TiO2 crystallites, but could also enhance the microstrain of TiO2. In terms of O2-TPD, a new adsorbed species O− appeared on the surface of La-doped TiO2. The results of in-situ Fourier transform-infrared (FT-IR) spectroscopy illustrated that the high activity of Au/La2O3-TiO2 was attributed to the presence of La promoting the reactivity of CO adsorbed on the Au site and the formation of the second active site on the surface of TiO2

Promoting effects of ceria on the catalytic performance of gold supported on TiO2 for low-temperature CO oxidation

The La or Ce-doped TiO2 prepared by a sol–gel method was used as the support, and supported gold catalysts for CO oxidation were prepared by the deposition–precipitation method. These Au catalysts were characterized by N2 adsorption–desorption, ICP, XRD, TEM, H2-TPR, and in situ FT-IR. It was found that doping Ce or La in the TiO2 support obviously improved the catalytic activity and stability of the Au catalysts for CO oxidation. The promoting effect of CeO2 on its catalytic activity is much larger than La2O3. The presence of Ce not only increases the surface area of TiO2 and restrains the growth of TiO2 crystallites, but it also enhances the microstrain of TiO2 and reinforces the interaction between TiO2 and Au. As a result of the redox efficiency of CeO2, the synergistic interaction between the Au particles and support, the activity of the active sites and the reactivity of the surface oxygen species, are remarkably improved. Moreover, the effortless decomposition of carbonates and the quick recovery of oxygen vacancies on the Au/Ce–TiO2 surface might be responsible for the high stability of the Au catalyst, compared with the Au/TiO2 catalyst.

Influence of the component interaction over Cu/ZrO2 catalysts induced with fractionated precipitation method on the catalytic performance for methanol steam reforming

A series of binary Cu/ZrO2 catalysts by choosing different composition ratios and different precipitation sequences have been prepared for the production of hydrogen by steam reforming of methanol (SRM). A variety of characterization techniques including N2 adsorption, N2O chemisorption, TEM, TPD and Raman are employed to characterize the physical and chemical properties of the catalysts. The results show that the preparation methods significantly affect the component dispersion, microstructure and adsorption properties. The Cu/ZrO2 catalyst with 27.3% ZrO2 loading prepared by fractionated precipitation method displays higher specific surface and interface between copper and zirconia, which not only accelerates decomposition of adsorbed methanol and water, but also promotes formation of Cu+ and surface oxygen species, accordingly enhancing the catalytic activity and stability.

A First‐Principles DFT Study on the Active Sites of Pd‐Cu‐Clx/Al2O3 Catalyst for Low‐Temperature CO Oxidation

Research on the CO low-temperature oxidation has been a hot and important topic with regard to commercial applications and academic interest. Commercially, it can be widely used, for example, in indoor air cleaning, automotive exhaust treatment, CO2 lasers, breathing apparatus, and fuel cells. In academia, findings and general laws established regarding CO oxidation will set solid foundations for the catalytic oxidation theory. For the catalysts used in low-temperature CO oxidation, water resistance and catalyst stability are still serious challenges, 2] including for the recently studied catalyst Pd-Cu-Clx/gAl2O3. [3–5] It is generally believed that the overall catalytic chemistry of supported Wacker-type catalysts for CO oxidation is similar to that of the homogeneous Wacker catalyst (Pd-CuClx), which is expressed in Equation (1): [6] COþ PdCl2 þ H2O! CO2 þ Pd þ 2 HCl ð1aÞ Pd þ 2 CuCl2 ! PdCl2 þ 2 CuCl ð1bÞ 2 CuClþ 2 HClþ 1=2 O2 ! 2 CuCl2 þ H2O ð1cÞ

The role of zirconia in cobaltosic oxide catalysts for low-temperature CO oxidation

A series of Co3O4/ZrO2 catalysts for low-temperature CO oxidation was prepared with different ZrO2 loadings and different preparation methods, and then characterized by low-temperature N2 adsorption/desorption, XRD, TEM, XPS, UV-vis, CO-TPR, CO adsorption and CO2 desorption. The results show that ZrO2 not only increases the specific area and decreases the crystal size of Co3O4 in CZ-c-20 and CZ-f-20, but also promotes production of Co2+ and –O−, which shows the high catalytic activity for CO oxidation. The facile decomposition of carbonate and the high redox properties over ZrO2 promote the catalytic stability for CO oxidation.