The Sabatier principle has been applied to nonuniform site ensembles of ZSM-5 catalysts of different compositions (Si/Al = 25, 36, and 135) during the induction period of the conversion of methanol and dimethyl ether to propylene. For the first time, site-specific volcano-plots and site-specific activity-maps have been observed following microkinetic simulations of the temperature-programmed surface reaction of methanol and dimethyl ether over ZSM-5 catalysts in a temporal analysis of products reactor. The microkinetic simulations are constructed using coupled 1D nonlinear partial differential equations that connect reactions at the active site to convection and dispersion through the reactor. The methoxymethyl cation pathway predicts the formation of propylene from methanol and dimethyl ether via dimethoxyethane. Site-specific scaling relations are observed between the acid site density and the barriers of the dissociative desorption of dimethyl ether with the barrier of methoxymethyl cation formation during the induction period of propylene formation from methanol and dimethyl ether, respectively. During the induction period of methanol conversion to propylene, depending on the barrier to methoxymethyl cation formation, the active site density should not be too low such that site cooperation is inhibited and not too high such that site competition is promoted. The optimum site density is ca. 5 × 10^–4 mmol g^–1 of active sites over the high-temperature active sites of ZSM-5 (Si/Al = 36) catalysts. Over the high-temperature active sites on ZSM-5 (25) catalysts, we observe a maximum rate of propylene formation at an optimum site density of 7 × 10^–4 mmol g^–1 active sites. During the induction period of dimethyl ether conversion, the binding energies should not be too weak to activate dimethyl ether and not too strong to inhibit its release into the gas phase. The binding energy of methoxymethyl cation should be between −80 kJ mol^–1 and −100 kJ mol^–1 for maximum propylene formation over the low-temperature active sites of ZSM-5 (Si/Al = 36) catalysts. Over the medium-temperature active sites of ZSM-5 (Si/Al = 36) catalysts, the maximum rate constant of propylene formation is observed between a binding energy of dimethyl ether of −135 kJ mol^–1 and −145 kJ mol^–1. The site-specific activity maps show that the catalytic activity of methanol-to-olefin conversion varies across the different site ensembles. In each site-specific activity map, the direction of the maximum rate constant of propylene formation changes with zeolite composition and site-ensemble. The precision given by this site-specific control shows that the catalytic activity can be tailored to the site characteristics.

中文翻译：

---

ZSM-5 催化剂上甲醇转化为烯烃过程中观察到的位点特异性活性图


在甲醇和二甲醚转化为丙烯的诱导期，Sabatier 原理已应用于不同组成（Si/Al = 25、36 和 135）的 ZSM-5 催化剂的非均匀位点集合。在产物反应器的时间分析中，对 ZSM-5 催化剂上甲醇和二甲醚的程序升温表面反应进行微动力学模拟后，首次观察到了特定地点的火山图和特定地点的活动图。微动力学模拟是使用耦合一维非线性偏微分方程构建的，该方程将活性位点的反应与反应器中的对流和扩散联系起来。甲氧基甲基阳离子途径预测甲醇和二甲醚通过二甲氧基乙烷形成丙烯。在甲醇和二甲醚生成丙烯的诱导期间，酸位点密度和二甲醚解离解吸势垒与甲氧基甲基阳离子形成势垒之间观察到了位点特异性比例关系。在甲醇转化为丙烯的诱导期，根据甲氧基甲基阳离子形成的势垒，活性位点密度不宜太低，以免抑制位点合作，也不宜太高，以免促进位点竞争。最佳站点密度约为。 ZSM-5 (Si/Al = 36) 催化剂的高温活性位点上有 5 × 10 ^–4 mmol g ^–1 活性位点。在 ZSM-5 (25) 催化剂的高温活性位点上，我们观察到在最佳位点密度为 7 × 10 ^–4 mmol g ^–1 活性位点时丙烯形成的最大速率网站。 在二甲醚转化的诱导期，结合能不能太弱而不能活化二甲醚，也不能太强以抑制其释放到气相中。甲氧基甲基阳离子的结合能应在 -80 kJ mol ^–1 和 -100 kJ mol ^–1 之间，以便在 ZSM-5 (Si/ Al=36)催化剂。在 ZSM-5 (Si/Al = 36) 催化剂的中温活性位点上，观察到丙烯形成的最大速率常数介于 -135 kJ mol ^–1 的二甲醚结合能和 - 145 kJ 摩尔 ^–1 。位点特异性活性图显示，甲醇转化为烯烃的催化活性在不同位点集合中存在差异。在每个位点特定活性图中，丙烯形成的最大速率常数的方向随着沸石组成和位点集合而变化。这种位点特异性控制给出的精度表明催化活性可以根据位点特征进行调整。