A comparative study on the effects of alkali metal on the structures, physico-chemical properties and catalytic behaviors of silica-supported vanadium catalysts for the selective oxidation of ethane and the complete oxidation of diesel soot was reported.

The redox and acid–base characters of silica-supported vanadium or alkali-modified vanadium catalysts by varying vanadium loading were studied with the methods of H2-TPR, NH3-TPD and CO2-TPD combining other structural characterization techniques of ESR, UV–vis spectroscopy. The effects of these properties on their catalytic performances for the ethane oxidation by oxygen were investigated. For both the unpromoted V/SiO2 (V:Si = x:Si) and promoted Cs–V/SiO2 (Cs:V:Si = 1:x:100) systems, the reduction extent and the reducibility increase with increasing vanadia loading and the presence of cesium enhances the reduction extent. The structures of the vanadyl species have large effect on the vanadia reducibility and the isolated surface vanadyl species are less reducible than the polymeric vanadyl species including microcrystalline vanadia. For the samples with high vanadia loading (≥2.0%), the reducibility is high and thus the redox characteristic of the catalyst is one of the most important factors that govern the catalytic reactivity. In the samples with low vanadia loading (<0.5%), the reducibility is low. Therefore, the basicity or acidity characteristics of the catalyst become the major factors that control the catalytic reactivity. The cesium promoted samples Cs–V/SiO2 (2.0 and 10.0%) exhibit high reducibilities, which qualitatively suggests that their oxygen mobility is very high and may result in deep oxidation of ethane. In contrast, those samples with low reducibility are selective for the oxidation of ethane including ODH to ethylene and oxygenate formation.

The nanometric La2-xKxCuO4 oxide catalysts with K2NiF4-type structure were prepared by auto-combustion method using citric acid as a ligand and an adjusting agent of particle-size and morphology. The structures and physico-chemical properties of these perovskite-like oxides were examined by means of XRD, FT-IR, H2-TPR and chemical analysis. The catalytic activities for the simultaneous removal of soot and NOx were evaluated by a technique of the temperature-programmed oxidation reaction (TPO). In the La2-xKxCuO4 catalysts, the partial substitution of K for La at A-site leads to the increase of the concentrations of Cu3+ and oxygen vacancy. Thus, it enhances the catalytic activity for simultaneous removal of NOx and diesel soot, and the optimal substitution amount of potassium x is equal to 0.5 among these samples. T10, T50, T90 are 376, 438,487 ℃ and PN2 is 22%, respectively, for simultaneous removal of NOx and soot particulates over the La1.5K0.5CuO4 catalyst under loose contact conditions between the catalyst and soot.

The CrHZSM-5 catalysts with trace amount of Cr were firstly used for catalytic cracking of isobutane, and the effect of Crloading on the catalytic performances of CrHZSM-5 catalysts for the cracking of isobutane was also studied. The results suggested that when the loading of Cr in the CrHZSM-5 catalysts was less than 0.038 mmol/g Cr, especially at Cr loading of 0.004 mmol/g, both the reactivity of isobutane cracking and the selectivity to light olefins of CrHZSM-5 samples were greatly enhanced compared with the unpromoted HZSM-5, and very high yields of olefins(C2+C3) and ethylene were obtained. For instance, the yield of olefins(C2+C3) and ethylene reached 56.1% and 30.8%, respectively, at 625 ℃ when 0.004 mmol/g Cr was loaded on HZSM-5sample.

Vanadium oxides supported on γ-Al2O3, SiO2, TiO2, and ZrO2 were studied on their molecular structures and reactive performances for soot combustion. To investigate the effect of different alkali metals on the structures and reactivities of supported-vanadium oxide catalysts, they were doped into the V4/TiO2 catalyst which had the best intrinsic activity for soot combustion in the selected supported vanadium oxide catalysts. The experimental results demonstrated that the catalytic properties of these catalysts depended on the vanadium loading amount, support nature, and the presence or the absence of alkali metals. The spectroscopic analysis (FT-IR and UV–vis) and H2-TPR results revealed that the higher activity of alkali-promoted vanadium oxide catalysts could be related to the ability of alkali metal promoting the redox cycle of the active vanadyl species. TG results showed that adding alkali to Vm/TiO2 catalyst was beneficial to lowering their melting points. Low melting points could ensure the good surface atom migration ability, which would improve the contact between the catalyst and soot. Due to the alkali metal components promoting the redox ability and the mobility of the catalysts, alkali-modified vanadium oxide catalysts could remarkably improve their catalytic activities for soot combustion. The catalytic activity order for soot combustion followed Li > Na > K > Rb > Cs in the catalyst system of alkali-V4/TiO2, and the reason why it followed this sequence was discussed.