Heqin Guo

Efficient V2O5/TiO2 composite catalysts for dimethoxymethane synthesis from methanol selective oxidation

A series of V2O5/TiO2 composite catalysts (V2O5–TiO2–Al2O3, V2O5–TiO2–SiO2, V2O5–TiO2–Ce2O3 and V2O5–TiO2–ZrO2) were prepared by an improved rapid sol–gel method and the catalytic behavior for dimethoxymethane (DMM) synthesized from methanol selective oxidation was investigated. The physicochemical properties of catalysts were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller isotherms (BET), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H2-TPR), NH3 temperature programmed desorption (NH3-TPD), infrared spectroscopy of adsorbed pyridine (Py-IR) and transmission electron microscopy (TEM) techniques. The best catalytic performance was obtained on a V2O5–TiO2–SiO2 catalyst with methanol conversion of 51% and DMM selectivity of 99% at 413 K. Furthermore, the V2O5–TiO2–SiO2 catalyst displayed an excellent catalytic stability within 240 h. Results showed that more Bronsted acidic sites were critical to increasing the DMM yield. The activity of V2O5/TiO2 composite catalysts decreased with increasing Bronsted acidity, but the yield of DMM increased with an increasing amount of Bronsted acidic sites. The excellent performance of the V2O5–TiO2–SiO2 catalyst might come from its optimal acidity and redox properties, higher active surface oxygen species, together with more Bronsted acid sites.

The one-step oxidation of methanol to dimethoxymethane over sulfated vanadia–titania catalysts: influence of calcination temperature

Sulfated vanadia–titania catalysts were prepared by the rapid combustion method and calcined at different temperatures. The influence of calcination temperature on the physicochemical properties of the catalysts was characterized by nitrogen adsorption (BET), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), inductively coupled plasma-optical emission spectroscopy (ICP-OES), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (H2-TPR-MS), thermogravimetry (TG) and temperature programmed desorption of ammonia (NH3-TPD) techniques. The catalytic activities were evaluated by the partial oxidation of methanol to dimethoxymethane (DMM). The results showed that vanadia and sulfate were highly dispersed as the catalysts were calcined at 723 and 773 K. The reducibility of the highly dispersed vanadia was stronger than the aggregated vanadia. And the larger number of acidic sites was related to the higher dispersion of sulfate. Moreover, the higher dispersion of vanadia contributed to higher methanol conversion, and the stronger reducibility combined with the larger number of acidic sites led to high DMM selectivity. As a result, the catalysts calcined at 723 and 773 K presented higher methanol conversion and DMM selectivity than those calcined at 673 K or above 823 K.

Elucidating the nature and role of copper species in catalytic carbonylation of methanol to methyl acetate over copper/titania–silica mixed oxides

In this study, a series of copper/titania–silica mixed oxide (Cu/TS) catalysts with different copper contents were prepared by a sol–gel method. The catalytic activity was evaluated by halide-free methanol carbonylation to methyl acetate (MA). The properties of the catalysts were mainly characterized by N2 adsorption–desorption, X-ray diffraction, dissociative N2O chemisorption, X-ray photoelectron spectroscopy, temperature-programmed desorption of ammonia and in situ Fourier transform infrared. The results show that the crystal size and aggregation degree of Cu increase with increasing Cu content. In addition, the amount of surface Cu+ firstly increases and then decreases, and the maximum is 1.560 mmol g−1 for the 10.24 Cu/TS catalyst. Both the amounts of adsorbed CO and surface Lewis acid sites are found to be proportional to the amount of surface Cu+ species. The catalytic performance shows that the space time yield (STY) of MA is also strongly related to the amount of surface Cu+ species, and the 10.24 Cu/TS catalyst has a maximum of 1.770 mol h−1 kgcat−1. It is found that the surface Cu+ species act not only as metal sites which adsorb CO but also as Lewis acid sites which promote the adsorption of methanol (methoxy). Furthermore, the activation of CO is the major factor for the MA synthesis.