Zhiming Liu

A superior catalyst with dual redox cycles for the selective reduction of NOx by ammonia

An environmentally benign Cu-Ce-Ti oxide catalyst exhibited excellent NH3-SCR activity, high N2 selectivity and strong resistance against H2O and SO2 with a broad operation temperature window. The dual redox cycles (Cu(2+) + Ce(3+) ↔ Cu(+) + Ce(4+), Cu(2+) + Ti(3+) ↔ Cu(+) + Ti(4+)) play key roles for the superior catalytic deNOx performance.

Recent advances in the selective catalytic reduction of NOx by hydrogen in the presence of oxygen

Selective catalytic reduction of NOx by hydrogen (H2-SCR) in the presence of oxygen has received much attention as a potential technology for reducing NOx emissions. A lot of research has been done in order to understand the reaction mechanism of H2-SCR and some possible mechanisms have been proposed. These mechanisms can be classified into two categories: NO adsorption/dissociation mechanisms and oxidation–reduction mechanisms. Based on the discussion of the reaction mechanism, the influence of the nature of the noble metal, catalyst support, catalyst preparation method, promoters and reaction conditions (including the presence of H2 and O2, water, sulfur, CO and CO2) on the catalytic performance of some H2-SCR catalysts has been discussed. Finally, future research directions in the area of H2-SCR have been proposed.

Effect of preparation method on the performance of Pt–Au/TiO2 catalysts for the catalytic co-oxidation of HCHO and CO

A series of TiO2 supported Pt–Au bimetallic catalysts were prepared by impregnation, deposition–precipitation and impregnation–deposition–precipitation, and their catalytic activities for the co-oxidation of formaldehyde (HCHO) and carbon monoxide (CO) were evaluated at room temperature. The results show that the Pt–Au/TiO2 catalyst prepared via introducing Pt by impregnation and subsequently introducing Au by deposition–precipitation, exhibits excellent catalytic performance for the co-oxidation of HCHO and CO. The characterizations of the catalyst by means of Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), Temperature Programmed Reduction (TPR) and in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (in situ DRIFTS) revealed that the isolated Pt and Au sites are essential to the co-oxidation of HCHO and CO, because the HCHO oxidation occurring over Pt active sites while CO oxidation occurring over Au active sites can be conducted without mutual interference, thus simultaneously achieving both the high oxidation activity of HCHO and CO.

In situ DRIFTS investigation of the promoting effect of Zr on Pd/Al2O3 catalyst for the catalytic combustion of methane

Surface species formed during the catalytic combustion of methane over Al2O3 supported Pd and Pd–Zr catalysts have been investigated by in situ DRIFTS techniques. It is found that formate and carbonate ions are formed during the reaction as intermediates, and the further oxidation of formate ion to carbonate ion requires reactive oxygen species supplied by activating gaseous oxygen at oxygen vacancies on the catalyst surface. Modification of Pd/Al2O3 catalyst by Zr addition leads to the increase of oxygen vacancy, which promotes the activation of gaseous oxygen and contributes to the oxidation of formate ion, resulting in a higher catalytic performance for the catalytic combustion of methane.

The effect of preparation conditions of Pt/Al2O3 on its catalytic performance for the H2-SCR in the presence of oxygen

Selective catalytic reduction of NOx by H2 in the presence of oxygen has been investigated over Pt/ Al2O3 catalysts pre-treated under different conditions. Catalyst preparation conditions exert significant influence on the catalytic performance, and the catalyst pre-treated by H2 or H2 then followed by O2 is much more active than that pre-treated by air. The higher surface area and the presence of metallic Pt over Pt/Al2O3 pre-treated by H2 or pretreated by H2 then followed by O2 can contribute to the formation of NO2, which then promotes the reaction to proceed at low temperatures.

Density Functional Theory Studies of NO and NO2 Adsorption on Al2O3 Supported SnO2 Cluster

AbstractThe adsorption of NO and NO2 on Al2O3(100), SnO2(110) as well as Al2O3(100) supported SnO2 cluster has been investigated using first principle density functional theory calculations. It was found that there is a strong interaction between the SnO2 cluster and the Al2O3(100) surface. The SnO2 cluster dispersed on the Al2O3 surface provides strong binding sites for the NOx adsorption. Compared with Al2O3(100) and SnO2(110) surfaces, both NO and NO2 adsorption and activation are promoted over the Al2O3(100) supported SnO2 cluster.Graphical AbstractAl2O3(100) supported SnO2 clustern.

Promoting effect of Zr on the catalytic combustion of methane over Pd/γ-Al 2 O 3 catalyst

The effect of Zr on the catalytic performance of Pd/γ-Al2O3 for the methane combustion was investigated. The results show that the addition of Zr can improve the activity and stability of Pd/γ-Al2O3 catalyst, which, based on the catalyst characterization (N2 adsorption, XRD, CO-Chemisorption, XPS, CH4-TPR and O2-TPO), is ascribed to the interaction between Pd and Zr. The active phase of methane combustion over supported palladium catalyst is the Pd0/Pd2+ mixture. Zr addition inhibits Pd aggregation and enhances the redox properties of active phase Pd0/Pd2+. H2 reduction could effectively reduce the oxidation degree of Pd species and regenerate the active sites (Pd0/Pd2+).