微乳法制备的Pt-B/Al_2O_3在对氯硝基苯加氢动力学上的研究

Preparation of Pt-B/Al_2O_3 via microemulsion and kenitics study of p-chloronitrobenzene hydrogenation

采用十六烷基三甲基溴化铵(CTAB)/正丁醇/环己烷/H2Pt Cl6溶液的微乳液体系制备了非晶态Pt-B/Al_2O_3催化剂,并对催化剂进行了TEM、SAED和XPS表征。以对氯硝基苯(p-CNB)选择加氢反应为探针,考察了微乳液体系中CTAB/正丁醇/环己烷质量比、微乳液体系中水相含量以及制备方法对催化剂加氢性能的影响,并进行了反应动力学研究。催化剂表征及催化加氢性能测试表明:与浸渍法相比,微乳液法制备的催化剂中Pt-B非晶态合金粒子粒径小且分布更加均匀,其p-CNB加氢反应的催化剂活性(以转换频率TOF表示)从0.065 s-1提高到0.166 s-1;当CTAB/正丁醇/环己烷质量比为16∶24∶60,微乳液体系中H2Pt Cl6溶液(w)4%时,单微乳液法制备的催化剂用于p-CNB加氢反应,p-CNB转化率为76.8%,p-CAN选择性为95.9%。动力学研究表明:p-CNB加氢反应近似为一级反应,其表观活化能为29.34 k J/mol。

Amorphous catalyst Pt-B/Al2O3 is prepared from a microemulsion system of cetyl trimethylammonium bromide （CTAB）/n-butanol/cyclohexane/H2PtCl6 solution, and the prepared catalyst is characterized by TEM, SAED and XPS. The effects of mass ratio of CTAB, n-butanol and cyelohexane in the microemulsion system, mass fraction of water in the microemulsion system, and preparation method on the catalytic hydrogenation performance of Pt-B/l2O3 catalyst are investigated using selective hydrogenation of p-chloronitrobenzene （p-CNB） as a probe, and the kenitics of p-CNB hydrogenation is also studied. The results of characterization and catalytic hydrogenation performance test show that comparing with the catalyst prepared by impregnation method, the one prepared by mieroemulsion has smaller and highly dispersed Pt-B particles with much higher catalytic activity, which increased from 0.065 s-1 to 0. 166 s-1（ represented by transform of frequency, TOF）. Under the conditions that the mass ratio of CTAB, n-butanol and eyelohexane is 16 ： 24 ： 60, and mass fraction of HEPtC16 in the microemulsion system is 4%, the catalyst prepared by mono microemulsion shows ex- cellent performance of p-CNB hydrogenation, the conversion of p-CNB reaches 76.8% and the selectivity of p-CAN reaches 95.9%. Kinetics study proves p-CNB hydrogenation as a first-order reaction with apparent activation energy of 29.34 kJ/mol.