以络合真空浸渍法制备了Pt-Sn-K/γ-Al_2O_3,催化剂.采用吡啶吸附红外光谱、CO脉冲吸附、程序升温还原、热重及程序升温氧化等手段对催化剂进行了表征,研究了K助剂对Pt-Sn-K/γ-Al_2O_3催化剂结构及其催化C_(16)正烷烃临氢脱氢反应性能的影响.结果表明,K的引入减弱了SnO_x和Al_2O_3间的相互作用,促进了Pt对SnO_x的还原,并导致催化剂的脱氢反应活性降低.K的加入还减少了强酸中心数目,一方面减少了催化剂酸性位上的副反应,提高了产物选择性;另一方面提高了催化剂的抗积炭能力,催化剂稳定性有所改善.但过量的K助剂减弱了催化剂的金属位-酸性位的协同作用,使得催化剂活性和稳定性均有所降低.
A Pt-Sn-K/γ-Al_2O_3 catalyst was prepared by complex impregnation under vacuum. The effect of the K promoter on the catalytic properties of the Pt-Sn-K/γ-Al_2O_3 catalyst for the dehydrogenation of long-chain paraffins to mono-olefins was investigated using n-hexadecane dehydrogenation as a test reaction. The catalyst was characterized by infrared spectroscopy of pyridine adsorption, CO pulse chemisorption, temperature-programmed reduction with H_2, thermogravimetric analysis, and temperature-programmed oxidation with O_2. The results show that the addition of K decreases the interaction of SnO_x and Al_2O_3, promotes the reduction of SnO_x species, and suppresses the catalyst activity for dehydrogenation. The K promoter also neutralizes the acidity and decreases the amount of strong acidic centers of the catalyst. Thus, the side reactions on the catalyst are inhibited, and the selectivity for monoolefins is increased. The stability of the catalyst is slightly enhanced with the addition of K because of the increased resistance to coke formation on the catalyst. However, the synergistic effect of active sites and acidic sites is weakened by the excess addition of the K promoter, which results in a great decrease in the activity and a low stability of the catalyst.
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