Relationship between the Acid-base Properties of Nitrogen-modified ZnO-ZrO2/SBA-15 Catalysts and Their Catalytic Performance in the Synthesis of 1,3-Butadiene from Ethanol
1,3-Butadiene(hereinafter referred to as butadiene),as an important organic intermediate in the chemical indus-try,has a wide range of uses in the petroleum and rubber industries.Using ethanol as raw material to produce butadiene can solve the non-renewable problem of raw materials,so it has received more and more attention.In this paper,catalysts were hydrothermally synthesized by using SBA-15 as the support,nitrate as the oxide precursor,and nitrogen-containing organic compounds as the additive.And then,the relationship between catalytic performance(ethanol conversion and butadiene yield)and the acid-base properties of catalysts was explored in the synthesis of butadiene from ethanol.Specifically,we used melamine(M),cyanuric acid(Ma),1,10-phenanthroline(Pm),imidazole(Im),and 1,3,5-triazine(St)as nitrogen-containing additives for the preparation of Zn-Zr/SBA-15+X catalysts.Through the activity evaluation of the catalysts,the activities of ethanol dehydrogenation and dehydration,acetaldehyde condensation,and Meerwein-Ponndorf-Verley(MPV)reactions were calculated.Then,by analyzing the dependence of these activities and butadiene yield on the acidity and basicity(the strength and number of acidic/basic sites)of catalysts,we found that appropriate amounts of weak acid(0.022 mmol·g-1),moderate acid(0.078 mmol·g-1),moderate base(0.055 mmol·g-1),and strong base(0.056 mmol·g-1)are helpful for the ethanol dehy-drogenation,whereas excess amount of weak acid and moderate acid will lead to the ethanol dehydration.Appropriate amounts of moderate acid(0.078 mmol·g-1)and moderate base(0.055 mmol·g-1)will favor the acetaldehyde condensation and MPV reactions.The butadiene yield is closely related to the activities of acetaldehyde condensation and MPV.The mel-amine-modified catalyst(Zn-Zr/SBA-15+M)has the optimum amounts of weak acid,moderate acid,moderate base,and strong base in accordance with the above quantities,resulting in the best catalytic performance:99.5％conversion of ethanol,65.5％selectivity of butadiene,and 0.45 gBD·gcat-1·h-1 of butadiene productivity.
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