Na对PtSn/ZSM-5催化丙烷脱氢反应性能的影响

以HZSM-5分子筛为载体, 利用分步浸渍法制得不同Na含量的PtSnNa/ZSM-5催化剂, 用于丙烷脱氢反应. 利用XRD、吡啶吸附红外光谱、NH3-TPD、氢化学吸附、TPR等手段, 研究了Na的添加对PtSn/ZSM-5催化剂物化性质的影响. 结果表明: Na的添加对PtSn/ZSM-5催化剂的反应性能影响明显. 适量Na的添加不仅降低了催化剂中的Brönsted酸中心和Lewis中强/强酸中心, 抑制了积碳的发生, 提高了催化反应的稳定性; 而且提高了催化剂表面的Pt金属裸露度, 增加了反应活性. 当Na含量为1.0%(w)时, 催化剂的丙烯选择性和收率达到最大, 反应30 h后, 丙烷转化率仍然保持很高(36.4%). 继续增加Na含量, 催化剂中的Lewis弱酸中心有所增加, 同时Sn组分易于被还原成Sn0, 丙烷裂解、氢解等副反应增加, 不利于脱氢反应的进行.

Effect of Na Addition on Catalytic Performance of PtSn/ZSM-5 Catalyst for Propane Dehydrogenation

PtSnNa/ZSM-5 catalysts with different amounts of Na were prepared by the sequential impregnation method on HZSM-5 zeolites, and their catalytic activities and stabilities in propane dehydrogenation were investigated. The effect of the addition of sodium on the physicochemical properties was studied by means of XRD (X-ray diffration), IR spectrum of adsorbed pyridine, NH3-TPD, H2 chemisorption, TPR (temperature-programmed reduction), etc. The results indicated that the addition of Na had an obvious impact on the catalytic performance of the PtSn/ZSM-5 catalyst. A suitable concentration of Na could not only reduce the Brönsted acid sites and moderate/strong Lewis acid sites, thus preventing the catalyst from coking and improving the catalytic stability, but also increase the fraction of bare metallic Pt on the surface of the catalyst, thus increase the catalytic activity. It was found that the propene selectivity and yield could reach the maximum, when the Na content was 1.0%(w). After reaction for 30 h, the propane conversion was still high (36.4%). However, the continuous addition of Na increased the weak Lewis acid sites and promoted the tin species to be reduced to metallic tin. In this instance, the cracking and hydrogenolysis of propane could be carried out easily, which was disadvantageous to the dehydrogenation.