CoMoW sulfide nanocatalysts for the HDS of DBT from novel ammonium and alkyltrimethylammonium-thiomolybdate-thiotungstate-cobaltate (II) precursors

Abstract

Five unsupported, highly active CoMoW trimetallic nanocatalysts were obtained by in situ decomposition from five novel precursors: (NH4)2[Co(MoS4)(WS4)] and (RN(CH3)3)2[(MoS4)(WS4)] (where R=dodecyl, tetradecyl, cetyl and octadecyl), during the HDS of DBT. The catalyst labeled CoMoWS-C14, derived from the precursor containing the tetradecyl group, exhibits the highest catalytic activity (k=421×10−7mol/gs). N2 adsorption–desorption shows that the CoMoW catalysts are mesoporous materials with characteristic Type IV isotherms, having surface areas of 11–340m2/g. Elemental analysis by X-ray energy dispersive spectroscopy (EDS) working at STEM mode finds high concentrations of carbon (3.7≤C/Mo≤11.3 and 2.7≤C/W≤9) in all the catalysts except CoMoWS, where carbon was not detected. The XRD patterns show that the catalysts are highly dispersed (less so for the CoMoWS) given the absence of the (002) reflection, along with broad and low intensity (101) and (110) reflections. High dispersion is also supported by the STEM micrographs showing unstacked layers. The selectivity of the reaction for all catalysts favors the direct desulfurization pathway. The surface area and high catalytic activity do not show direct correlation with the length of the hydrocarbon chains of the precursors.