Perez-Aguilar Jorge E, Chen Cong-Yan, Hughes James T, Fang Chia-Yu, Gates Bruce C
Department of Chemical Engineering, University of California, Davis, California 95616, United States.
Chevron Energy Technology Company, Richmond, California 94802, United States.
J Am Chem Soc. 2020 Jul 1;142(26):11474-11485. doi: 10.1021/jacs.0c03730. Epub 2020 Jun 19.
Zeolites are widely applied supports for metal catalysts, but molecular sieves with comparable structures-silicoaluminophosphates (SAPOs)-have drawn much less attention and been overlooked as supports for atomically dispersed metals. Now, we report SAPO-37 as a support for atomically dispersed rhodium in rhodium diethylene complexes, made by the reaction of Rh(η-CH)(acetylacetonate) with the support and anchored by two Rh-O bonds at framework tetrahedral sites, as shown by infrared and extended X-ray absorption fine structure spectra. The ethylene ligands were readily replaced with CO, giving sharp ν bands indicating highly uniform supported species. A comparison of the spectra with those of comparable rhodium complexes on zeolite HY shows that the SAPO- and zeolite-supported complexes are isostructural, providing an unmatched opportunity for determining support effects in catalysis. The two catalysts had similar initial room-temperature activities per Rh atom for ethylene conversion in the presence of H, but the SAPO-supported catalyst was selective for ethylene hydrogenation and the zeolite-supported catalyst selective for ethylene dimerization; correspondingly, the catalyst on the SAPO was more stable than that on the zeolite during operation in a flow reactor.
沸石是金属催化剂广泛应用的载体，但具有类似结构的分子筛——硅铝磷酸盐（SAPOs）——作为原子分散金属的载体受到的关注要少得多，且一直被忽视。现在，我们报道了SAPO - 37作为铑二乙烯配合物中原子分散铑的载体，它是通过Rh(η-CH)(乙酰丙酮)与载体反应制备的，并通过两个Rh - O键锚定在骨架四面体位置，红外光谱和扩展X射线吸收精细结构光谱表明了这一点。乙烯配体很容易被CO取代，产生尖锐的ν带，表明负载物种高度均匀。将这些光谱与在HY沸石上的类似铑配合物的光谱进行比较表明，SAPO负载和沸石负载的配合物是同构的，这为确定催化中的载体效应提供了无与伦比的机会。在H存在下，这两种催化剂对于乙烯转化，每个Rh原子具有相似的初始室温活性，但SAPO负载的催化剂对乙烯加氢具有选择性，而沸石负载的催化剂对乙烯二聚具有选择性；相应地，在流动反应器中运行期间，SAPO上的催化剂比沸石上的催化剂更稳定。
