Steering the reaction pathway of syngas-to-light olefins with coordination unsaturated sites of ZnGaOx spinel

Abstract

Significant progress has been demonstrated in the development of bifunctional oxide-zeolite catalyst concept to tackle the selectivity challenge in syngas chemistry. Despite general recognition on the importance of defect sites of metal oxides for CO/H2 activation, the actual structure and catalytic roles are far from being well understood. We demonstrate here that syngas conversion can be steered along a highly active and selective pathway towards light olefins via ketene-acetate (acetyl) intermediates by the surface with coordination unsaturated metal species, oxygen vacancies and zinc vacancies over ZnGaOx spinel−SAPO-34 composites. It gives 75.6% light-olefins selectivity and 49.5% CO conversion. By contrast, spinel−SAPO-34 containing only a small amount of oxygen vacancies and zinc vacancies gives only 14.9% light olefins selectivity at 6.6% CO conversion under the same condition. These findings reveal the importance to tailor the structure of metal oxides with coordination unsaturated metal sites/oxygen vacancies in selectivity control within the oxide-zeolite framework for syngas conversion and being anticipated also for CO2 hydrogenation.

Combustion, Chemistry, and Carbon Neutrality

“…The complexity of such reaction processes is evident e.g., from the investigation of Li et al on C 2 –C 4 light olefin production from syngas using a specific ZnGaO x spinel catalyst . To characterize the catalyst, understand the nature and formation of intermediates, the roles of chemisorbed species, lattice vacancies, and coordination sites, and to describe the mechanism toward a specific product spectrum, a multitude of techniques were combined including HRTEM, SEM, helium ion microscopy (HIM), XRD, EDXS, inductively coupled plasma optical emission spectroscopy (ICP-OES), in situ ambient pressure (AP) X-ray photoelectron spectroscopy (XPS), quasi in situ electron paramagnetic resonance (EPR) and photoluminescence (PL) spectroscopy, temperature-programmed desorption and reduction (TPD, TPR), in situ FTIR, and online GC . Advanced experimental techniques, − ,− , numerical simulations, ,,,− ,,, and/or theoretical methods ,,, have been refined and applied to such heterogeneous reaction systems, and concurrently, methodologies and computational tools have been described to systematically develop and analyze microkinetic mechanisms, ,− also using machine learning and automated mechanism generation approaches. , …”

Unveiling the Anti-Trap Effect for Bridging Intermediates on ZnAlOx/AlPO-18 Bifunctional Catalysts to Boost Syngas to Olefin Conversion

“…The higher selectivity of the target products and the shorter reaction process seem to make it more competitive. Inspired by this pioneering work, a series of bifunctional catalysts containing different oxide and zeolite components have been widely exploited and tested. − …”

“…The driving forces of push and pull rendered by individual oxide and zeolite components contribute to the catalytic activity and selectivity. The design of bifunctional catalysts should thus be focused on the balance of both driving forces by optimizing the composition and structure of oxides, ,− tuning the acidity and topology of zeolites, − and modulating the migration behavior of bridging intermediates …”

Comprehensive Study of Oxygen Vacancies on the Catalytic Performance of ZnO for CO/H2 Activation Using Machine Learning-Accelerated First-Principles Simulations

“…Syngas (CO/H 2 ) is an important intermediate platform for the utilization of carbon resources such as coal, natural gas, and biomass, which can be converted into a variety of high-value chemicals and fuels. , Great efforts have been devoted to understanding the reaction mechanisms of syngas conversion. It is generally believed that methanol synthesis through CO hydrogenation catalyzed by Cu/ZnO/Al 2 O 3 follows a sequential hydrogenation mechanism to formyl and methoxy intermediates and eventually methanol .…”