摘要
考察了浸渍法制备的高分散Pt-Ti/Al_2O_3催化剂中Ti对Pt活性中心的调变作用。用脉冲反应技术,以C_6烷烃反应分子为探针,基于三元环和环化机理,根据反应产物分布的变化和TEM方法表征的结果,推断Ti的加入,可以改变Pt中心的电子特征。Ti与Pt中心相互作用,使Pt中心富集电子,脱氢能力减弱,反应总活性下降,明显地抑制了氢解反应,而脱氢环化选择性增高。
Pt-Ti/Al2O3 catalysts were prepared by sequential depositing Ti2-(SO4)3 and H2PtCl6 in A12O3 by incipient wetness impregnation, and were used to study the effect of Ti on Pt sites in the catalytic reaction of C6 alkane with hydrogen. Prior to use, catalysts were treated in air at 300℃ and then reduced in hydrogen at 450℃. The composition and Pt particle size of the catalysts were measured by an atomic emission spectroscopy and a high resolution transmission electron microscope respectively. A pulse microreader with an attached FID gas chromatograph was used to study the catalytic reaction. The effects of Ti on Pt are. (1) Pt-Ti/Al2O3 shows a much lower activity than Pt/Al2O3 for all the reaction of C6 alkanes studied; (2) the overall activation energies are lower over the bimetallic catalysts; (3) the selectivities for hydrogeno-lysis, isomerization and cyclization are depressed, slightly enhanced and quite enhanced respectively; (4) the bond fission probabilities during hydrogenolysis are changed, i.e. there is a larger probability for bond fission at the bond adjacent to a more electron deficient C atom, it is considered that this electronic effect as an electron donation to Pt weakens the dehydrogenation ability of Pt and also leads to an increase in 1, 3 bond shift probability in isomerization.
