Wenhuai Li

Mesoporous HMS molecular sieves supported cobalt catalysts for Fischer–Tropsch synthesis

Abstract Hexagonal mesoporous silica (HMS), Al-HMS, MCM-41, as well as ZrO2 modified HMS supported cobalt and small amount of MnO promoted cobalt catalysts are investigated by using X-ray diffraction, N2 adsorption, transmission electron microscopy, and temperature programmed reduction techniques, and by testing their catalytic properties in Fischer–Tropsch synthesis. Cobalt oxides are dispersed highly on the surface of these mesoporous supports. However, their BET surface area, pore volume, and pore size decrease, and pore wall thickness increases a little. The main hydrocarbon products obtained over these catalysts are the long chain hydrocarbons (wax). Comparing with MCM-41 and Al-HMS, the HMS supported Co catalyst shows better catalytic activity and C5+ selectivity, which is due to its smaller domain size with shorter channels and larger textural mesoporosity. With increasing Co loading on the HMS support, the reduction temperature of cobalt oxides increases a little, but the activity apparently increases, which is caused by more active sites in the channels of HMS. When Al-HMS is used as a support, the interaction between Co species and Al-HMS support caused by the acid properties on the surface of Al-HMS, leads to a decrease of available Co metal sites and a decrease of activity and C5+ selectivity. The pre-impregnated ZrO2 on the surface of HMS support favors the reduction of cobalt oxides and increases the activity and C5+ selectivity. The addition of small amount of Mn (⩽2 wt.%) to Co/HMS catalyst, high yield of wax (36.2%) is obtained, which might be ascribed to that MnO segregates partially the active Co sites and prevents the formation of methane at high reaction temperature.

Nickel and manganese co-modified K/MoS2 catalyst: high performance for higher alcohols synthesis from CO hydrogenation

Abstract Mn and Ni co-modified K/MoS2 catalyst for higher alcohols synthesis from syngas was prepared by co-precipitation, and its performance in CO hydrogenation was tested. The results indicated a synergistic effect between Mn and Ni on co-modified K/MoS2 catalyst, which led to high performance for higher alcohols synthesis.

XPS study of potassium-promoted molybdenum carbides for mixed alcohols synthesis via CO hydrogenation

Abstract The X-ray photoelectron spectroscopy (XPS) was used to investigate the surface characteristic of potassium-promoted or un-promoted both β-Mo2Cand α-MoC1−x pretreated by syngas at different temperatures, and the promotional effect of potassium on the catalytic performance was also studied. XPS results revealed that the content of surface Mo and its valence distribution between β-Mo2Cand α-MoC1−x were quite different. Promoted by potassium, the remarkable changes were observed for surface composition and valence of Mo distribution over β-Mo2C. Potassium had strong electronic effect on β-Mo2C, which led to a higher Mo4+ content. On the contrary, potassium had little electronic effect on α-MoC1−x, and K-Mo interaction was weak. Therefore, Mo0 and Mo2+ became the dominant species on the catalyst surface, and the Mo4+ content showed almost no increase as the pretreatment temperature enhanced. In terms of catalytic performance of molybdenum carbides, the increase in Mo0 most likely explained the increase in hydrocarbon selectivity, yet Mo4+ might be responsible for the alcohols synthesis.

Growth of segmented ZnS nanocones induced by regular occurrence of twins structure

Segmented ZnS nanocones have been prepared at 1200 degrees C by thermal evaporation of zinc sulfide powders and catalyst metal tin. The as-synthesized products have been studied by energy-dispersive x-ray spectroscopy, selected-area electron diffraction, and high-resolution transmission electron microscopy. Microstructure characterization indicates that the formation of segmented nanocones can be attributed to the effects of regular twins structure. Theoretical analysis reveals that the nonuniform cross sections of nanocones are related to the continuous change of Sn-ZnS liquid droplets scale resulting from the supply of Sn atoms during the evaporation. According to microstructure characterization and dimension analysis, the potential formation mechanism of the segmented ZnS nanocones was discussed

Nickel and potassium co-modified β-Mo2C catalyst for CO conversion

Abstract Nickel and potassium co-modified β-Mo2C catalysts were prepared and used for CO hydrogenation reaction. The major products over β-Mo2C were C1–C4 hydrocarbons, only few alcohols were obtained. Addition of potassium resulted in remarkable selectivity shift from hydrocarbons to alcohols at the expense of CO conversion over β-Mo2C. Moreover, it was found that potassium enhanced the ability of chain propagation with a higher C2+OH production. Modified by nickel, β-Mo2C showed a relatively high CO conversion, however, the products were similar to those of pure β-Mo2C. When co-modified by nickel and potassium, β-Mo2C exhibited high activity and selectivity towards mixed alcohols synthesis, and also the whole chain propagation to produce alcohols especially for the stage of C1OH to C2OH was remarkably enhanced. It was concluded that the Ni and K had, to some extent, synergistic effect on CO conversion.