Selective oxidation of methanol to dimethoxymethane over V 2 O 5 /TiO 2 –Al 2 O 3 catalysts

Highly efficient and durable syngas production over one-step synthesized synergistic oxygen carriers in biomass chemical looping gasification

Biomass chemical looping gasification (BCLG) gives a promising platform for cost-effective and low-polluting syngas production. To overcome the cumbersome process and poor dispersion of two-step synthesized synergistic oxygen carriers (OCs), NiO-LaFeO3 synergistic OCs were synthesized in one-step by sol-gel method with the found best Ni introduction amount of 0.5. The high lattice oxygen mobility and powerful oxidation capacity derived from the Ni-Fe synergistic effect made it perform better in the BCLG reaction. Due to the extraordinary stability of crystalline phase and oxygen activity, its reactivity did not suffer from any degradation during the 50 long-time redox cycles over 2750 min under the optimal working conditions of the ex-situ configuration, mutual mode and steam/biomass mass ratio of 5.0. The gas yield, carbon conversion, syngas selectivity and H2/CO ratio were constantly maintained around 1846.45 mL/g, 86.74%, 79.96% and 2.0, respectively. This study provides a feasible technical route for highly efficient and durable syngas production.

The Promoting Effect of Ti on the Catalytic Performance of V-Ti-HMS Catalysts in the Selective Oxidation of Methanol

The effects of Ti modification on the structural properties and catalytic performance of vanadia on hexagonal mesoporous silica (V-HMS) catalysts are studied for selective methanol-to-dimethoxymethane oxidation. Characterizations including N2 adsorption–desorption (SBET), X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS UV-Vis), Micro-Raman spectroscopy, FTIR spectroscopy, and H2 temperature-programmed reduction (H2-TPR) were carried out to investigate the property and structure of the catalysts. The results show that Ti can be successfully incorporated into the HMS framework in a wide range of Si/Ti ratios from 50 to 10. Ti modification can effectively improve the distribution of vanadium species and thus enhance the overall redox properties and catalytic performance of the catalysts. The catalytic activity of the V-Ti-HMS catalysts with the Si/Ti ratio of 30 is approximately two times higher than that of V-HMS catalysts with comparable selectivity. The enhanced activity exhibited by the V-Ti-HMS catalyst is attributed to the improved dispersion and reducibility of vanadium oxides.

First principles studies on the selectivity of dimethoxymethane and methyl formate in methanol oxidation over V2O5/TiO2-based catalysts

First principles calculations using both molecular cluster and periodic slab models were performed to reveal the mechanism for the formation of dimethoxymethane (DMM) from methanol over V₂O₅/TiO₂-based catalysts. Two different pathways were found, and the formation of DMM was predicted to be initiated by methanol chemisorption followed by a dehydration reaction with hemiacetal catalyzed by acidic sites. For unpromoted V₂O₅/TiO₂ catalysts, we predicted the energy barrier for the rate determining step (RDS) to follow the order formaldehyde (FA) > methyl formate (MF) > DMM, consistent with the experimental observation for the preferential formation of DMM at a relatively low temperature and that of MF at a relatively high temperature. For sulfate-promoted catalysts, the energy barriers were calculated to follow the order FA > DMM > MF, so the sulfate promoter was predicted to mainly enhance the selectivity of MF, consistent with our previous experiment in which very high yield of MF was obtained with the sulfate-promoted catalyst. Calculated rate constants for the RDS were further used for semi-quantitative predictions of the product selectivities, which were found to be in quite good agreement with some of the recent experimental data in the literature, showing the validity of our approach. We also investigated the effects of the titania support and the polymerization of the vanadia species on the reactivity of the V₂O₅/TiO₂ catalyst. Finally, we benchmarked several popular exchange-correlation functionals for calculating the reaction energies for the formation of FA, MF, and DMM from methanol oxidation, and the M06 hybrid functional was found to be superior to other semi-local and hybrid functionals studied.