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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. [ABSTRACT FROM AUTHOR]

Methanol-to-olefins (MTO), the most important catalytic process producing ethylene and propylene from non-oil feedstocks (coal, natural gas, biomass, CO2, etc.), is hindered by rapid catalyst deactivation due to coke deposition. Common practice to recover catalyst activity, i.e. removing coke via air combustion or steam gasification, unavoidably eliminates the active hydrocarbon pool species (HCPs) favoring light olefins formation. Density functional theory calculations and structured illumination microscopy reveal that naphthalenic cations, active HCPs enhancing ethylene production, are highly stable within SAPO-34 zeolites at high temperature. Here, we demonstrate a strategy of directly transforming coke to naphthalenic species in SAPO-34 zeolites via steam cracking. Fluidized bed reactor-regenerator pilot experiments show that an unexpectedly high light olefins selectivity of 85% is achieved in MTO reaction with 88% valuable CO and H2 and negligible CO2 as byproducts from regeneration under industrial-alike continuous operations. This strategy significantly boosts the economics and sustainability of MTO process. Methanol-to-olefins is hindered by rapid catalyst deactivation due to coke deposition. Here the authors demonstrate an approach of directly transforming coke to active intermediates to simultaneously recover catalyst activity and boost light olefins selectivity. [ABSTRACT FROM AUTHOR]

Mass transfer of guest molecules has a significant impact on the applications of nanoporous crystalline materials and particularly shape‐selective catalysis over zeolites. Control of mass transfer to alter reaction over zeolites, however, remains an open challenge. Recent studies show that, in addition to intracrystalline diffusion, surface barriers represent another transport mechanism that may dominate the overall mass transport rate in zeolites. We demonstrate that the methanol‐to‐olefins (MTO) reaction can be modulated by regulating surface permeability in SAPO‐34 zeolites with improved chemical liquid deposition and acid etching. Our results explicitly show that the reduction of surface barriers can prolong catalyst lifetime and promote light olefins selectivity, which opens a potential avenue for improving reaction performance by controlling the mass transport of guest molecules in zeolite catalysis. [ABSTRACT FROM AUTHOR]

Direct visualization of spatiotemporal evolution of molecules and active sites during chemical transformation in individual catalyst crystal will accelerate the intuitive understanding of heterogeneous catalysis. So far, widespread imaging techniques can only provide limited information either with large probe molecules or in model catalyst of large size, which are beyond the interests of industrial catalysis. Herein, we demonstrate a feasible deep data approach via synergy of multiscale reaction-diffusion simulation and super-resolution structured illumination microscopy to illustrate the dynamical evolution of spatiotemporal distributions of gas molecules, carbonaceous species and acid sites in SAPO-34 zeolite crystals of several micrometers that are typically used in industrial methanol-to-olefins process. The profound insights into the inadequate utilization of activated acid sites and rapid deactivation are unveiled. The notable elucidation of molecular reaction-diffusion process at the scale of single catalyst crystal via this approach opens an interesting method for mechanism study in materials synthesis and catalysis. Imaging zeolites in catalysis relies on the use of probe molecules or model catalysts. Here the authors show the synergy of a multiscale reaction-diffusion model and structured illumination microscopy to illustrate spatiotemporal evolution of molecules and acid sites in SAPO-34 zeolites in methanol-to-olefins reaction. [ABSTRACT FROM AUTHOR]

A coke distribution model of catalyst particles in three‐dimensional space was developed based on population balance theory, and an analytic expression of coke distribution for zero‐dimensional time‐independent problem was deduced. The expression shows that the coke distribution is determined by the average catalyst residence time, coke deposition (or burning) rate, and coke distribution of catalyst inflow. The coke distribution model was further applied to the methanol to olefins (MTO) process. The critical factors influencing coke distribution in MTO process, as well as the effect of coke distribution on product selectivity, were investigated. Three scales of MTO fluidized bed reactor–regenerator systems, i.e., pilot‐scale, demonstration‐scale and commercial‐scale with the reactor diameter of 0.261, 1.25, and 10.5 m, respectively, were simulated. The simulated results were in good agreement with the operation data. The model could be helpful in the operation optimization and reactor design. © 2018 American Institute of Chemical Engineers AIChE J, 65: 1149–1161, 2019 [ABSTRACT FROM AUTHOR]

[Display omitted] • BPO 4 with in-situ Brønsted acid sites was employed for glycerol dehydration. • BPO 4 shows high acrolein yield of 80 % and robust stability during 425 h test. • In-situ Brønsted acid site is highly selective for the secondary hydroxyl groups. • The construction of B[3] and P[4] defects is a prerequisite for the active site. Dehydroxylation of biomass-based platform molecules is critical for obtaining building blocks for use in the chemical industry. Acid catalytic dehydration has provided a feasible route. However, simultaneously pursuing high product-selective and ultra-stable catalysts for the dehydroxylation of polyols remains an open challenge. In this study, a strategy for in-situ Brønsted acid sites (BAS) with chemo-adsorption selectivity is proposed. The construction of defect sites B[3] and P[4] species has been proved to be a prerequisite for the dynamic acid site formation at hydrothermal conditions. The BPO 4 catalyst with in-situ BAS can achieve the high selectivity of acrolein (∼80%) and robust stability of catalyst (over 425 h) using glycerol dehydration as a model reaction. In addition, in-situ BAS is highly selective for secondary hydroxyl groups and has been extended to other substrate applications. This catalytic strategy provides a green, efficient, and economical approach for converting biomass-derived polyols to high-value-added chemicals. [ABSTRACT FROM AUTHOR]