载体对Pt/WO_3-ZrO_2催化临氢异构反应性能的影响

Effect of supports on the catalytic performance of Pt/WO_3-ZrO_2 catalysts for hydroisomerization

以平衡吸附过氧钨酸的水合氧化锆为前驱体,经焙烧得到WO_3-ZrO_2固体酸,并采用XRD、UV-vis、NH_3-TPD等手段考察了过氧钨酸吸附液浓度及焙烧温度对WO_3-ZrO_2固体酸组成、结构及酸性的影响。通过BET、H_2-TPR、H_2-TPD等表征手段和正戊烷临氢异构反应,考察了负载铂后相应催化剂的结构、还原与氢吸附性质及其催化正戊烷临氢异构反应的性能。结果表明,焙烧温度为700℃时,随着吸附液浓度的增加,所得载体酸度及相应催化剂比表面积均先增加后减小,且在吸附液浓度为82 mmol W/L时达到最大值。吸附液浓度为59 mmol W/L时,随着焙烧温度的升高,所得载体四方相氧化锆含量、酸度及相应催化剂比表面积均降低。吸附液浓度为82 mmol W/L、焙烧温度为700℃所得载体负载0.5%(质量分数)铂后催化活性最高。该催化剂在250℃常压临氢操作、n(H_2)/n(n-C_5H_(12))为3、WHSV为1.0 h^(-1)的条件下,催化正戊烷异构反应中异戊烷收率可达57.7%。

A series of WO3-ZrO2 solid acids were synthesized by calcining the equilibrium adsorbed peroxotungstic acid/hydrated zirconia precursors.The influences of peroxotungstic acid concentration and calcination temperature on the composition, structure and acidity of the obtained solid acids were evaluated by using XRD, UV-vis and NH3-TPD.Pt/WO3-ZrO2 catalysts were prepared by impregnation method and characterized by BET, H2-TPR and H2-TPD.The catalytic performance in the hydroisomerization of n-pentane was investigated.It was found that under the same calcination temperature, both the support acidity and the catalyst surface area first increase and then decrease with the increase of peroxotungstic acid concentration, and are maximized when the peroxotungstic acid concentration reaches 82mmol W/L.When the peroxotungstic acid possesses the same concentration of 59mmol W/L, the tetragonal zirconia fraction, support acidity and the catalyst surface area decrease with the increase of calcination temperature.When the peroxotungstic acid concentration and the calcination temperature of the support are 82mmol W/L and 700℃ respectively, the obtained catalyst shows the best catalytic performance.The yield of isopentane reaches 57.7% under the reaction condition of ambient pressure, 250℃, n（H2）/n（n-C5H12） =3 and WHSV =1.0h-1.