The Active Nature of Crystal MoS2 for Converting Sulfur-Containing Syngas

摘要

Molybdenum disulfides are attractive sulfur-tolerant catalysts suitable for the direct conversion of sulfur-containing syngas, which avoids the expensive step of the deep desulfurization. However, the catalytic activity of MoS2-based catalysts is relatively low. To improve the activity, previous works have focused on modifying MoS2 with various promoters and supports, but the structural aspects are largely overlooked. In this work, we investigated the active nature of the MoS2-based catalysts for the catalytic hydrogenation of carbon monoxide. Thus, the bulk MoS2 with varied crystallite sizes was synthesized by the hydrothermal and the thermal decomposition methods. The catalysts before and after catalytic tests were characterized by in-situ X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscope techniques. The CO hydrogenation under low-temperature methanation conditions (The syngas with a H-2/CO=2 and 40.0 ppm H2S, T=360 degrees C, and P=2 MPa) was applied to evaluate MoS2 as a catalyst for converting syngas. The catalytic results indicate that the MoS2 with smaller crystallite sizes exhibited a higher CO conversion. By correlating the structural propriety with the catalytic activity, a hexagonal-prim-shaped model was developed to describe different sites on the MoS2 crystallite. Based on this model, the activity of different active sites on the bulk MoS2 for CO hydrogenation decreased in the order of rim sites edge sites basal sites. The highest catalytic activity over the bulk MoS2 with smallest particles was attributed to the highest exposure of the rim sites.