NiWS/Al2O3 hydrotreating catalysts prepared with 12-tungstophosphoric heteropolyacid and nickel citrate: Effect of Ni/W ratio

Effect of Ni/W ratio on Ni-CA-PW/Al2O3 hydrotreating catalysts prepared with 12-tungstophosphoric heteropolyacid (PW-HPA) and nickel citrate was investigated. For comparison, the reference samples were prepared using nickel salt of PW-HPA and co-impregnating solution of ammonium metatungstate and nickel nitrate. All synthesized catalysts were characterized by N-2 physisorption, X-ray powder diffraction, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The catalytic properties were determined using a fixed-bed microreactor in hydrotreating of dibenzothiophene, naphthalene and quinoline. It was found that with the rise of Ni content in the prepared Ni-PW/Al2O3 catalysts the composition and morphological characteristics of the NiWS active phase species as well as their catalytic properties were changed simultaneously. Turnover frequency (TOF) number in all studied reactions increased with the decrease in both the average length of the NiWS phase species and Ni/W ratio in the (Ni)WS2 edges. Both NiW reference catalysts had active sites with lower TOF values than their counterparts prepared using PW-HPA and nickel citrate. The highest TOP values were achieved at moderate Ni/(Ni + W) ratio equal to 0.24. However, maximal conversions of the reactants were observed over the catalysts with higher Ni/(Ni + W) ratio equal to 0.33-0.45. The possible reasons of these changes are discussed in the paper. (C) 2015 Elsevier B.V. All rights reserved.