Relationship between surface characteristics and catalytic properties of unsupported nickel-tungsten carbide catalysts for the hydrocracking of vacuum residue

•The surface structure of the NiWC(x) is strongly affected by the Ni/(Ni + W) ratio.•The hydrogen adsorption is closely related to catalytic activity of NiWC(x).•NiWC(20) with an optimum Ni/(Ni + W) ratio showed the highest catalytic activity. The catalytic activity of tungsten carbide is known to resemble that of platinum. In a previous study, we found that the catalytic activity of tungsten carbide was influenced by its particle size. Alternatively, adding an appropriate amount of nickel to tungsten could increase the activity of tungsten carbide; however, detailed characterization was not performed to explain the enhanced catalytic activity from the addition of Ni. In this study, it was confirmed that hydrogen adsorption on the catalyst surface was strongly affected by the ratio of Ni/(Ni + W) on unsupported NiWC catalysts. When Ni was added, the adsorption of hydrogen and the carburization degree of NiWC increased; however, it was also observed through various analytical techniques — including XPS and H2-TPD — that the strong adsorption of hydrogen induced by WC was reduced. The negative effect of Ni addition was also observed; the addition of nickel could cause surface carbon deposition and severe aggregation of particles. Hence, an optimum ratio of Ni/(Ni + W) is required to maximize the catalytic activity of NiWC. In this study, the characteristics and catalytic activities of Ni-added tungsten carbide catalysts on the hydrocracking of vacuum residue were investigated using different Ni/(Ni + W) ratios. As a result, the yield of commercial liquid was maximized, and coke formation was significantly reduced for the NiWC(20) catalyst with a Ni/(Ni + W) ratio of 23 mol.%.