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(η2-C2H4)2(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 νCO 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 H2, 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.

中文翻译：

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负载在 SAPO-37 和 HY 沸石上的同构原子分散铑催化剂

沸石是金属催化剂的广泛应用载体，但具有类似结构的分子筛——硅铝磷酸盐 (SAPO)——却很少受到关注，并被忽视作为原子分散金属的载体。现在，我们报告 SAPO-37 作为铑二乙烯配合物中原子分散铑的载体，由 Rh(η2-C2H4)2(乙酰丙酮) 与载体反应制成，并由框架四面体位点的两个 Rh-O 键锚定，如红外和扩展 X 射线吸收精细结构光谱所示。乙烯配体很容易被 CO 取代，产生尖锐的 νCO 带，表明支持的物质高度均匀。将光谱与沸石 HY 上可比的铑配合物的光谱进行比较表明，SAPO 和沸石负载的配合物是同构的，为确定催化中的支持效应提供了无与伦比的机会。在 H2 存在下，两种催化剂每个 Rh 原子对乙烯转化的初始室温活性相似，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反应具有选择性；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。