Metal substitution in aluminophosphates is known to induce unique structural and surface characteristics that can tune catalytic performance. Si, Co, Fe and Mg substituted AlPO₄-5 (MeAPO-5) catalysts were hydrothermally prepared, characterized, and evaluated for ethanol - acetic acid esterification. Textural evaluation revealed that the Co and Si analogues possessed an order of magnitude higher mesopore volume compared to the rest of the studied materials. Divalent metal ions (i.e. Co, Fe, and Mg) substituted preferentially Al ions via the SM1 mechanism, as confirmed by the P/Al being greater than one, while Si ions substituted P ions (SM2) initially, followed by substitution of pairs of Al-P ions (SM3) at higher Si content. The esterification catalytic activity was found to follow the order SAPO-5 > > CoAPO-5 > MgAPO-5 $\approx$ FeAPO-5. The superior performance of SAPO-5 is ascribed to the higher concentration of Brønsted acid sites and faster mass transfer rates due to the relatively small crystal size and larger fraction of mesopores. Notably, the SAPO-5 with the optimal Si content demonstrated comparable stability against deactivation within the range of reaction conditions studied and sustained catalytic activity at prolonged reaction durations when compared to commercial Zeolite β, despite the significantly higher surface area, pore volume and density of acid sites of the latter, primarily attributed to less strong adsorption of the reaction products. The reported parametric results for various metal substitutions shed light towards optimizing aluminophosphate catalysts for esterification applications.

众所周知，铝磷酸盐中的金属取代会引起独特的结构和表面特征，从而可以调节催化性能。硅，钴，铁和镁取代的AlPO ₄水热制备-5（MeAPO-5）催化剂，进行表征，并进行乙醇-乙酸酯化评估。结构评价表明，与其余研究材料相比，Co和Si类似物的中孔体积高一个数量级。二价金属离子（例如，Co，Fe和Mg）通过SM1机理优先取代了Al离子，这已被P / Al大于1证实，而Si离子最初取代了P离子（SM2），随后成对的取代Si含量较高的Al-P离子（SM3）。发现酯化催化活性遵循以下顺序：SAPO-5>> CoAPO-5> MgAPO-5$\approx$FeAPO-5。SAPO-5的卓越性能归因于较高的布朗斯台德酸位点浓度和更快的传质速率，这是由于相对较小的晶体尺寸和较大的中孔分数所致。值得注意的是，与商用沸石β相比，具有最佳Si含量的SAPO-5在研究的反应条件范围内具有相当的抗失稳性，并且在延长的反应持续时间内具有持续的催化活性，尽管其表面积，孔体积和密度显着更高。后者的酸性位点，主要归因于反应产物较弱的吸附。报道的各种金属取代的参数结果为优化用于酯化应用的磷酸铝催化剂提供了启示。