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

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 <i>ca.</i> 1 μm. The maxima of the quantity <i>vs</i>. 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.