The Effect of Cr, Ni, Fe, and Mn Dopants on the Performance of Hydrothermal Synthesized Vanadium Phosphate Catalysts for n-Butane Oxidation

摘要

Vanadium phosphorus oxide (VPO) catalysts synthesized via hydrothermal method were introduced with some different dopants, Cr, Ni, Fe, and Mn during the preparation of the precursors, VOHPO_4 0.5H-2O. All modified precursors were subsequently transformed under reaction conditions to give the active phase, (VO)_2P_2O_7. Several techniques were used to characterize the physicochemical properties of the catalysts, such as X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), H2-temperature programmed reduction (TPR), laser Raman spectroscopy (LRS), and chemical analysis. The catalytic performance of the catalysts for selective oxidation of n-butane to maleic anhydride has been carried out by using a fixed bed microreactor (673 K, gas hourly space velocity [GHSV] D 2,400 hr~(-1)). The results show that the addition of dopants into the VPO catalysts increased the surface area of the catalysts and induced the formation of V~(5+) phases as shown in XRD and LRS spectra that promoted the catalytic performance. A further water reflux treatment to all the precursors gave catalysts with only (VO)_2P_2O_7 phase. However, the activity and selectivity of these catalysts were reduced markedly.