Effect of composition and promoters in Au/TS-1 catalysts for direct propylene epoxidation using H2 and O2
Effect of composition and promoters in Au/TS-1 catalysts for direct propylene epoxidation using H2 and O2
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DOI：
10.1016/j.cattod.2008.09.005
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发表时间：
2009-10
期刊：
影响因子：
5.3
通讯作者：
Jiqing Lu;Xiaoming Zhang;Juan J. Bravo-Suárez;T. Fujitani;S. Oyama
中科院分区：
文献类型：
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作者：
Jiqing Lu;Xiaoming Zhang;Juan J. Bravo-Suárez;T. Fujitani;S. Oyama
采用沉积-沉淀法（DP）制备了一系列碱金属和碱土金属离子促进的Au/钛硅分子筛TS-1（TS-1）催化剂，并考察了其丙烯直接环氧化反应性能。结果发现，金负载量和催化活性是高度依赖于DP合成溶液的pH值和催化剂的最终组成。添加第1族金属如K或Cs对金含量影响不大，但增加了活性，而第2族金属如Mg、Ca、Sr和Ba增加了金含量和催化活性。Mg促进的催化剂提供了最高的改进，其在443 K和0.1 MPa下，H2/O2/C3 H6/Ar=1/1/1/7进料混合物得到88 gPOh − 1 kgcat −1的环氧丙烷（PO）形成速率，相比之下，未促进的催化剂为57 gPOh − 1 kgcat − 1，对应于50%的活性增强。氨程序升温脱附（NH3-TPD）的测量结果表明，吸附量的变化不大，促进表明，产率的增加是由于在催化剂上的酸性位点的消除。相反，改进的催化性能归因于催化剂增加的Au捕获效率和分散。硅/钛比、合成pH值和助催化剂离子对金含量的影响可以从它们对载体表面电荷的影响来理解。
A series of Au/titanium silicalite-1 (TS-1) catalysts with different Si/Ti ratios and promoted with alkali and alkaline earth cations were prepared by deposition–precipitation (DP) and tested for direct propylene epoxidation. It was found that the gold loading and catalytic activity was highly dependent on the pH of the DP synthesis solution and the final composition of the catalyst. Addition of Group 1 metals such as K or Cs had little effect on the gold content, but increased activity, while Group 2 metals such as Mg, Ca, Sr, and Ba increased both the gold content and the catalytic activity. The highest improvement was provided by a Mg promoted catalyst, which at 443K and 0.1MPa with a H2/O2/C3H6/Ar=1/1/1/7 feed mixture gave a propylene oxide (PO) formation rate of 88gPOh−1kgcat−1, compared to 57gPOh−1kgcat−1for an unpromoted catalyst, corresponding to a 50% enhancement of activity. Ammonia temperature-programmed desorption (NH3-TPD) measurements indicated little change in adsorption amount with promotion indicating that the yield increase was not due to the elimination of acidic sites on the catalyst. Instead, the improved catalytic performance was ascribed to increased Au capture efficiency and dispersion by the catalyst. The effect of Si/Ti ratio, pH of synthesis, and the promoter ions on the gold content could be understood from their effect on the surface charge of the support.