Cu/ZnO Catalysts Derived from Bimetallic Metal–Organic Framework for Dimethyl Ether Synthesis from Syngas with Enhanced Selectivity and Stability

Abstract

Syngas can be produced from natural gas, shale gas, coal, biomass, and organic wastes. [1,2] Through a versatile "Fischer-Tropsch synthesis (FTS)" process, syngas can be transformed into valuable chemicals, such as hydrocarbons (gasoline, diesel fuel, light olefins, and aromatics) and oxygenates (alcohols and ether). [3] One of the most attractive oxygenate products from FTS process is dimethyl ether (DME) given its eco-friendly properties. DME is both a promising alternative of diesel fuel with higher cetane number (between 55 and 60) and low soot emission as well as an important feedstock for the production of methyl acetate, fuel cells, and aromatics. [4] DME production has traditionally been realized via a two-step process, where methanol is first synthesized from syngas and then dehydrated to DME. However, the first step, methanol synthesis, is limited by the thermodynamic constraints and as a result, the overall CO conversion is relatively low. As an alternative to such process, a one-step process, where direct "syngas-to-DME (STD)" conversion occurs in a single reactor via consecutive methanol synthesis and methanol dehydration reactions, has been developed. Compared to the two-step process, the STD Direct conversion of syngas to dimethyl ether (DME) through the intermediate of methanol allows more efficient DME production in a simpler reactor design relative to the conventional indirect route. Although Cu/ZnObased multicomponent catalysts are highly active for methanol synthesis in this process, the sintering issue of Cu during the prolonged reaction generally deteriorates their performance. In this work, Cu/ZnO catalysts in a novel octahedron structure are prepared by a two-step pyrolysis of Zn-doped Cu-BTC metal-organic framework (MOF) in N 2 and air. The catalyst CZ-350/A, hybrid of MOF-derived Cu/ZnO sample CZ-350 and γ-Al 2 O 3 for methanol dehydration, displays the best activity for DME formation (7.74% CO conversion and 70.05% DME selectivity) with the lowest deterioration rate over 40 h continuous reaction. Such performance is superior to its counterpart CZ-CP/A made via the conventional coprecipitation method. This is mainly due to the confinement of Cu nanoparticles within the octahedron matrix hindering their migration and aggregation. Besides, partial reduction of ZnO in the activated CZ-350 prompts the formation of Cu + -O-Zn, further facilitating the DME production with the highest selectivity compared to literature results. The results clearly indicate that Cu and ZnO distribution in the catalyst architecture plays an important role in DME formation.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.

Investigation on the promotional role of Ga2O3on the CuO–ZnO/HZSM-5 catalyst for CO2hydrogenation

“…Both of the spectra contained two peaks at about 1022 and 1045 eV ( Fig. 6B ), which are assigned to Zn 2p 3/2 and Zn 2p 1/2 peaks of ZnO, 38 respectively, with a spin energy separation of 23 eV. This shows that zinc atoms are present in the catalyst in the form of ZnO.…”

Electrochemical performance of asymmetric device using the nickel–zinc organometallic structure

“…[ 47,48 ] Figure 3b suggests that the Zn 2p XPS sample has functional peaks at 1021.98 and 1044.98 eV, assigned to Zn 2p 3/2 and Zn 2p 1/2 , correspondingly, and the splitting forces among Zn 2p 3/2 and Zn 2p 1/2 are 23 eV, suggesting that zinc is in the ionic form and that BTC is in the complex bridge form. [ 49,50 ]…”

Engineering of Yolk/Core–Shell Structured Nanoreactors for Thermal Hydrogenations

“…[ 72 ] Similarly, a bifunctional Cu/ZnO/γ‐Al 2 O 3 nanoreactor was reported for highly selective conversion of syngas to dimethyl ether while a core‐shell Cu‐MOR@SiO 2 nanoreactor was designed for conversion of syngas and dimethyl ether to ethanol. [ 73,74 ] This demonstrates the effectiveness of the synergistic effects achieved by proper modification of the core–shell structure. SiO 2 has been used to modify a Al 2 O 3 @Al‐supported cobalt catalyst to increase heat transfer and reduce metal–support interaction, as well as improve cobalt reduction.…”