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The preparation of vanadium-phosphate catalysts by Atomic Layer Deposition (ALD) was studied for application to selective oxidation of n-butane to maleic anhydride (MA). Modification of bulk V2O5 by ALD with trimethylphosphate significantly increased the selectivity to MA but the catalyst performance was still much worse than that observed for bulk vanadium phosphate (VPO). Silica-supported VPO was then prepared by ALD of P and V and compared to a VPO/SiO2 catalyst prepared by impregnation. Raman spectra showed that the ALD-prepared materials were more homogeneous, and temperature-programmed desorption of 2-propanol demonstrated that the VPO phase covered the silica more uniformly when deposited by ALD. However, the bulk VPO catalyst remained the most selective for MA. Possible reasons for why the supported catalysts showed lower performance are discussed and suggestions made for improving these catalysts. [ABSTRACT FROM AUTHOR]

Nitrogen oxides (NO_x), as one of the main atmospheric pollutants, seriously affect environmental safety and human health. Selective catalytic reduction (NH_3-SCR) is the most effective treatment method for NO_x removal at present, especially low-temperature SCR denitrification technology, which has very important application prospects and research significance. The research showed that VPO/TiO_2 catalyst had excellent low-temperature SCR denitrification activity. The adsorption of NH_3 and NO on V_2O_5 and (VO)_2P_2O_7 surface was simulated by DFT, and the reaction mechanism of VPO catalyst was studied at the micro level. The results showed that NH_3 exhibited stable chemisorption of Brønsted acid and Lewis acid on the surface of V_4P_4O_22H_14 cluster, and the adsorption effect on Brønsted acid sites was more stable. NH_3 adsorption effect on the surface of catalyst was excellent because of the hybridization of 2p orbital of N, 2p of O and 3d electron orbital of V. NO also showed chemisorption on the surface of V_4P_4O_22H_14 cluster. Due to the small amount of electron transfer, which was significantly lower than the adsorption energy of NH_3, NO could not strongly compete with NH_3 molecule. In addition, NO showed stable chemisorption on Brønsted acid and Lewis acid on the surface of V_6O_20H_10 cluster. The adsorption on Brønsted acid sites was more stable. The E-R mechanism and L-H mechanism of VPO/TiO_2 catalyst reaction mechanism were explained.

Vanadium phosphorus oxide (VPO) was immobilized on SBA-15 via a facile impregnation process. The structure and VPO species on SBA-15 were characterized by XRD, TEM, BET, FTIR and XPS techniques. It was found the VPO/SBA-15 catalysts maintained the two-dimensional hexagonal structure of SBA-15, and the supported VPO species existed in a highly dispersed amorphous state. VPO/SBA-15 catalyst was tested for the ammoxidation of dichlorotoluenes (DCTs) to corresponding dichlorobenzonitriles (DCNs) in a lab-scale tube reactor. Compared with VPO/SiO2 (large-pore silica-supported VPO), VPO/SBA-15 exhibited appreciable enhancement in the catalytic performance due to the unique channel structure of SBA-15. The yield and selectivity toward 2,4-DCN increased by 7% and 6%, while toward the sterically hindered 2,6-DCN increased by 7% and 13%, respectively. [ABSTRACT FROM AUTHOR]