Influence of formation temperature on the morphology of MoS2 and its catalytic properties in the hydrogenation of isomeric bromoquinolines to bromo-1,2,3,4-tetrahydroquinolines†

Abstract

Eight samples of MoS₂ were prepared by the hydrothermal reaction of paramolybdates with thiourea where the synthesis temperature was varied from 120 to 180 °C. It was shown by XPS and Raman spectroscopy that the samples mainly consisted of MoS₂ but contained significant quantities of oxidized species. All samples had a flower-like morphology, as evidenced by TEM and SEM. The flower-like structure was built of nanosheets aggregated in conglomerates with sizes ranging from 50 nm to ca. 1 μm. The maxima of the quantity vs. size distribution curves of such conglomerates gradually shifted to higher values upon an increase in formation temperatures. All samples were catalytically active in the hydrogenation of quinoline; however, the highest yields of 1,2,3,4-tetrahydroquinoline were achieved for the MoS130–MoS145 samples. The hydrogenation of the isomeric bromo-substituted quinolines in the presence of MoS130–MoS140 was examined. In these cases, the respective bromo-1,2,3,4-tetrahydroquinolines were formed with high selectivity, except for 6-bromoquinoline. The results of the study may be applied to the development of selective catalysts for the hydrogenation of halogen-containing aromatic compounds.