Studies On Conversion Of Syngas Over Hierarchical Zeolite Y-supported Co-Mn Catalyst

Due to the depletion of petroleum resources,the development of catalytic processes for the transformation of nonpetroleum carbons feedstocks such as coal,natural(also shale gas),and biomass into clean liquid fuels and chemicals for energy production has attracted much attention.Fischer-Tropsch(FT)synthesis,that is,the synthesis of hydrocarbons by hydrogenation of CO,is a key process for the conversion of versatile carbon feedstocks to fuels via syngas.Although FT synthesis has a long history.some key scientific challenges still remain for fundamental research.One of the most important but difficult challenges is selectivity control.It is demonstrated that developing bifunctional catalyst could improve the selectivities of middle-fraction fuels in FT synthesis.Based on this strategy,we developed the Co/Na-meso-Y catalysts and studied the effect of promoter on catalytic performance on FT synthesis,then investigated the influence of hydrogenolysis reaction over these catalysts,and further revealed the relationship between catalyst properties and catalytic performances of FT synthesis.We first studied the promoter effects on Co/Na-meso-Y catalysts.The results showed that the addition of Mn promoter could impro-ve the selectivities to C10-20(diesel fuel)and C5+ hydrocarbons by suppressing the formation of CH4 and light hydrocarbons(C2-C4).Over the Co-Mn/Na-meso-Y catalyst with Mn/Co ratio of 0.21,the CO conversion was 33%,and the selectivities to C5+ and C10-20 hydrocarbons were 91%and 65%,respectively.After 1000 h of reaction,the product selectivity remained almost unchanged.Moreover,the increase in the Mn/Co ratio increased the selectivity to C10-C15 hydrocarbons and decreased those to CH4 and C5-C9 hydrocarbons for hydrogenolysis reaction of n-hexadecane.Thus,we speculate that the contribution of hydrogenolysis would improve the selectivities to diesel fuel by limited the selectivities of CH4 in FT synthesis over the catalyst with a proper Mn loading.The reduction degree of Co species gradually decreased with an increase in the ratio of Mn/Co.At the same time,the amounts of H2 chemisorption also gradually decreased.The dispersion of Co particles evaluated from the H2 chemisorption also became lower in the catalyst with a larger Mn/Co ratio.It is reasonable to speculate that the interaction between Co and Mn species retarded the reduction of Co species.Finaly,the activity for n-hexadecane hydrogenolysis was suppressed.In the FT synthesis.The reduction of Co(Mn/Co>0.21)which is less than 60%,leads to the decrease in carbon chain growth factor(a),arid thus increases the selectivity to CH4.