Density-functional theory (DFT) study of arsenic poisoning of NiMoS

Abstract Arsenic poisoning of NiMoS hydrotreating catalysts was studied using density-functional theory (DFT) calculations. The incorporation of arsenic into NiMoS by chemical adsorption and dissociation of organoarsenic molecules (AsH 3 , (CH 3 ) 3 As, (C 2 H 5 ) 3 As, and (C 6 H 5 ) 3 As) and the substitution of Ni and S atoms by arsenic on both fully promoted Ni(1 0 0)Mo- and Ni(1 0 0)S-edge surfaces were investigated. DFT calculation results show that the adsorption of organoarsenic compounds is energetically favored on both surfaces and there is a correlation between the adsorptivity of the arsenic compounds and their electronic structure. After the organoarsenic molecules have adsorbed on the edge surfaces, dissociation on a Ni(1 0 0)S-edge surface is energetically favored. Arsenic may substitute Ni atoms on both Ni(1 0 0)Mo-edge and Ni(1 0 0)S-edge surfaces. However, the substitution of S atoms by arsenic may only occur on the Ni(1 0 0)S-edge surface. The DFT results are compared with previously reported EXAFS studies on arsenic deposited NiMoP/Al 2 O 3 hydrotreating catalysts.