Direct propylene epoxidation over modified Ag/CaCO3 catalysts
Direct propylene epoxidation over modified Ag/CaCO3 catalysts
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DOI：
10.1016/j.apcata.2006.01.023
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发表时间：
2006-04
影响因子：
5.5
通讯作者：
Jiqing Lu;Juan J. Bravo-Suárez;M. Haruta;S. Oyama
中科院分区：
文献类型：
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作者：
Jiqing Lu;Juan J. Bravo-Suárez;M. Haruta;S. Oyama
本文研究了一系列负载型银催化剂在丙烯环氧化反应中的催化性能。结果表明，α-Al_2O_3和CaCO_3是丙烯环氧化反应的适宜载体，在CaCO_3上，400 ~ 700 nm的Ag颗粒具有最高的环氧丙烷（PO）选择性。CaCO 3催化剂的球磨处理和NaCl的促进导致催化性能的改善。当银负载量为56 wt.%时，催化剂的PO选择性最高（45负载在CaCO 3上，并用1 wt.% NaCl（Ag（56）-NaCl（1）/CaCO3）。在反应物流速为C3 H6：O2：He=5：10：15 cm 3 min-1、气时空速（GHSV）为1800 h-1、反应压力为0.3MPa和反应温度为533 K（260°C）的条件下测试催化剂。在反应气体中加入500 ppm的氯乙烷（EtCl）可提高Ag（56）-NaCl（1）/CaCO_3催化剂的稳定性。Ag（56）-NaCl（1）/CaCO 3催化剂的X射线衍射（XRD）检测到AgCl在催化剂中的存在，紫外-可见（UV-vis）漫反射光谱证实了表面Ag+物种的存在。扫描电子显微镜显示，通过球磨处理以及通过添加NaCl的Ag颗粒的粗糙化。NaCl对催化剂性能的增强作用可能是由于催化剂的物理和电子性质的变化。NaCl不仅有助于增加银在CaCO 3载体上的分散，而且可能增加了有利于环氧化反应的亲电氧物种的数量。原位紫外-可见光谱表明，Ag（56）-NaCl（1）/CaCO 3催化剂表面Ag+物种的快速还原可能是导致PO选择性下降的原因。
In this work a series of supported Ag catalysts was studied for propylene epoxidation with molecular oxygen as the oxidant. It was found that α-Al2O3and CaCO3were suitable supports for propylene epoxidation and that on the latter Ag particles between 400 and 700nm gave the highest selectivity to propylene oxide (PO). Ball-milling treatment of the CaCO3catalyst and promotion with NaCl resulted in improved catalytic performance. The highest PO selectivity (45%) was obtained on a ball-milled catalyst with a silver loading of 56wt.% supported on CaCO3and promoted with 1wt.% NaCl (Ag(56)–NaCl(1)/CaCO3). The catalysts were tested with reactant flow rates of C3H6:O2:He=5:10:15cm3min−1, a gas hourly space velocity (GHSV) of 1800h−1, a reaction pressure of 0.3MPa, and a reaction temperature of 533K (260°C). Addition of 500ppm of ethyl chloride (EtCl) to the reactant gases enhanced the stability of the Ag(56)–NaCl(1)/CaCO3catalyst. X-ray diffraction (XRD) of the Ag(56)–NaCl(1)/CaCO3catalyst detected the existence of AgCl in the catalyst and ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy confirmed the presence of surface Ag+species. Scanning electron microscopy showed a roughening of the Ag particles by the ball-milling treatment as well as by the addition of NaCl. The effect of NaCl on the enhancement of the catalytic performance was probably due to both physical and electronic changes in the properties of the catalyst. The NaCl not only helped increase the dispersion of the silver on the CaCO3support, but also probably increased the quantity of electrophilic oxygen species favorable for epoxidation. In situ UV–vis spectra suggested that the rapid reduction of Ag+species on the surface of the Ag(56)–NaCl(1)/CaCO3catalyst could be the cause of a decline in PO selectivity observed during reaction.