Microkinetic analysis of acetylene hydrogenation over Pd-Ag/Al2O3 catalyst with different Pd/Ag ratios

doi:10.11949/j.issn.0438-1157.20171007

Abstract

Abstract:

Selective acetylene hydrogenation is an important purifying reaction in ethylene industry. Pd-Ag/α-Al₂O₃ catalysts with different Pd/Ag ratios were prepared by stepwise incipient wetness impregnation method and characterized for structure and composition by N₂-physisorption,XRD,ICP,XPS,TEM and CO chemisorption. A microkinetic model of acetylene hydrogenation over these catalysts was established from a fractional factorial design of experiment and effects of Ag amount on the hydrogenation kinetics were analyzed through microkinetic simulation and parameter value change. After values for basic parameters used DFT calculation results of C₂ hydrogenation over Pt-Ag catalysts and activation energies optimized by adsorption-desorption steps, the microkinetic model could fit kinetic experiment results quite well on acetylene hydrogenation over all catalysts of various Pt-Ag ratios. The study showed that C₂H₄^* was the most abundant surface species and vinyl hydrogenation was rate control step, which did not change with increase of Ag content. However, the increase of Ag greatly reduced activation energy of hydrogen desorption and improved ethylene selectivity. This phenomenon might be correlated to enhancement of electron transfer from Ag to Pd on the catalyst surface upon increase of Ag content.

Key words: acetylene hydrogenation, Pd-Ag catalyst, microkinetic modeling, Ag effect

摘要：

乙炔加氢是乙烯工业中的重要精制反应。以α-Al₂O₃作为载体，采用分步等量浸渍法制备了不同Pd/Ag配比的加氢催化剂，使用N₂物理吸附、XRD、ICP、XPS、TEM和CO化学吸附等手段表征催化剂的结构和组成，根据正交实验设计方案进行动力学实验，建立了微观反应动力学模型，并根据动力学模拟结果和动力学参数值的变化分析了Ag助剂含量对乙炔加氢反应动力学的影响。研究结果表明，以Pd-Ag催化剂上碳二加氢的DFT计算结果为基础参数来源，经过吸脱附步骤活化能的优化，微观反应动力学模型可以很好地模拟不同Pd/Ag配比催化剂上的乙炔加氢反应动力学结果；在所研究范围内，各催化剂上加氢反应的表面最丰物种皆为C₂H₄^*，速率控制步骤为乙烯基加氢，不会随着Ag含量的不同发生变化；但是Ag含量的增加显著降低了氢气脱附活化能，提高了乙烯的选择性，这可能与Ag含量的提高增加了催化剂表面Ag和Pd之间的电子转移现象有关。

关键词: 乙炔加氢, Pd-Ag催化剂, 微观反应动力学, Ag助剂影响

CLC Number:

TQ032.4

ZHANG Jian, HUANG Bangyin, SUI Zhijun, ZHOU Xinggui, YUAN Weikang. Microkinetic analysis of acetylene hydrogenation over Pd-Ag/Al₂O₃ catalyst with different Pd/Ag ratios[J]. CIESC Journal, 2018, 69(2): 674-681.

张健, 黄邦印, 隋志军, 周兴贵, 袁渭康. 不同Pd/Ag配比Pd-Ag/Al₂O₃催化乙炔加氢微观反应动力学分析[J]. 化工学报, 2018, 69(2): 674-681.

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Microkinetic analysis of acetylene hydrogenation over Pd-Ag/Al₂O₃ catalyst with different Pd/Ag ratios

不同Pd/Ag配比Pd-Ag/Al₂O₃催化乙炔加氢微观反应动力学分析

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