Quantitative principle of shape‐selective catalysis for a rational screening of zeolites for methanol‐to‐hydrocarbons

Abstract

The production of hydrocarbons for the synthesis of readily available energy and multifunctional materials is of great importance in modern society. Zeolites have proven to be a boon for the targeted regulation of specific hydrocarbon as shape‐selective catalyst in converting carbon resources. Yet our mechanistic understanding and quantitative description of shape‐selectivity of zeolite catalysis remains rather limited, which restricts the upgrade of zeolite catalysts. Herein, we proposed quantitative principle of shape‐selectivity for zeolite catalysis using methanol‐to‐hydrocarbons (MTH) as model. Combining with molecular simulations and infrared imaging, we unveil the competition of thermodynamic stability, preferential diffusion and favored secondary reactions between different hydrocarbons within zeolite framework are the essence of zeolite shape‐selective catalysis. Notably, we provide methodology to in silico search for the optimal combination of framework topology and acidity properties of zeolites with operating conditions that potentially outperform commercial MTH catalysts to achieve high selectivity of desired hydrocarbon products.

Cavity-controlled methanol conversion over zeolite catalysts

“…Zeolite catalysts with various cavity structures mediate the reaction performance by changing the formation of crucial intermediates, olefin precursors and their involvement route in the complex reaction network based on the strong host–guest interaction of the supramolecular system, which jointly affect the MTO reaction's product selectivity. The cavity environment directly controls product distribution of the MTO reaction over cavity-type and small-pore zeolite and zeotype materials [ 34 , 38–40 ]. Liu and coworkers [ 38 ] established the definitive correlation between the catalyst's cavity structure and product selectivity by assessment of all the elementary steps of the complete catalytic cycles at the molecular level, and found that predominant formation of olefin products depended on the generation of HCP species, the formation of the olefin precursor and the reaction route together were mediated by different cavity-type zeolite or zeotype catalysts.…”

“…Furthermore, recently, Liu and coworkers [ 34 ] presented a quantitative shape selectivity for zeolite catalysis, which involves thermodynamics, reaction kinetics and molecular diffusion in a confined zeolite framework. The product’s distribution derives from the competitive effect of molecular diffusion and secondary reactions between hydrocarbon compounds, the ratio of selectivity of C y = /C 2 = and alkane/alkene.…”

“…Shape-selective catalysis is ubiquitous in the complete MTO reaction course [ 22 , 23 ], reflected by the formation of organic intermediates in the confined space [ 24 ], the special reaction mode for olefin product formation [ 25 , 26 ], deactivation with coke accommodation [ 27 , 28 ], reactant and products diffusion [ 29–32 ] and even the elementary steps in the reaction pathway of the complicated reaction network [ 18 , 33–35 ]. Notably, the microenvironment of zeolites embedding unique channel/cavity structure and acid properties has been taken as the dominant factor in the shape-selective catalysis process [ 34 , 35 ]. Especially for the 8-MR and cavity-type zeolites applied in the industry, the MTO reaction is significantly influenced by the cavity size and spatial confinement effect provided by the cavity-type catalyst.…”

“…As shown in Fig. 2 , the confined reaction intermediates and coke species in the zeolite cavity microenvironment, the preferential reaction routes in the complex reaction network, the catalyst deactivation and molecule diffusion join into cavity-controlled methanol conversion and drive the dynamic evolution of the MTO reaction [ 33 , 34 ]. During the process of methanol conversion, the ‘cavity-controlled principle’ is defined as a cage effect that originates from the unique cavity structure of zeolites, enabling precise control over the reaction intermediates, pathways, deactivation and diffusion.…”