Manganese Oxide Modified Nickel Catalysts for Photothermal CO Hydrogenation to Light Olefins

Abstract

from FTS reactions include light olefins, [2] higher hydrocarbons, methanol, [3] ethylene glycol, [4] dimethyl ether, [5] and aromatics. [6] Among all the products of FTS, light olefins (ethene, propene, and butene) are perhaps the most valuable and widely used in the production of fine chemicals, plastics, coatings, and cosmetics. [7] In FTS, the most commonly used catalysts are group VIIIB transition metals, especially iron, cobalt, nickel, and ruthenium. These catalysts differ in their CO hydrogenation activity and product selectivity, with several of these metals often being used together (in alloy form) to achieve a high CO conversion or to enhance the selectivity toward a specific product or group of products. Iron-based catalysts show good initial selectivity toward light olefins during FTS. [8] During FTS, metallic iron is gradually transformed to iron carbide during reaction (which is considered the true active phase of iron-based FTS catalysts). Iron carbide has a relatively mild hydrogenation ability and the ability to promote CC coupling reactions. However, FTS over iron-based catalysts typically requires temperatures above 300 °C, which can lead to coke formation and sintering of active sites, leading to catalyst deactivation. Co-based catalysts are suitable for CO hydrogenation to Ni-based catalysts are traditionally considered unsuitable for the Fischer-Tropsch syntheses of olefins, due to the very strong hydrogenation ability of metallic Ni. Herein, this paradigm is challenged. A series of MnO supports nickel catalysts (denoted herein as Ni-x) are fabricated by H 2 reduction of a nickel-manganese mixed metal oxide at temperatures (x) ranging from 250 to 600 °C. The Ni-500 catalyst displays unprecedented performance for photothermal CO hydrogenation to olefins, with an olefin selectivity of 33.0% under ultraviolet-visible irradiation. High-resolution transmission electron microscopy, X-ray absorption spectroscopy (XAS), and X-ray diffraction analyses reveal that the Ni-x catalysts contain metallic Ni nanoparticles supported by MnO. X-ray photoelectron spectroscopy and XAS establish that electron transfer from MnO to the Ni 0 nanoparticles is responsible for modifying the electronic structure of nickel (creating Ni δ− states), thereby shifting the CO hydrogenation selectivity toward light olefins. Further, density functional theory calculations show that this electron transfer lowers the adsorption energies of olefins on Ni surfaces, thus minimizing the undesirable deep hydrogenation reactions to higher alkanes. This study conclusively demonstrates that MnO-modified Ni-based catalyst systems can be highly selective for CO hydrogenation to light olefins.

Fundamentals and applications of photo-thermal catalysis

“…Very recently another paper from Zhang and co-workers was published, in which they reported the use of an unusual metal for the Fischer-Tropsch process: nickel. 228,229 Wang et al fabricated a novel class of catalysts, consisting of Ni NPs supported on manganese oxide (MnO), labelled Ni-x, where ''x'' represents the temperature at which the Ni-Mn mixed metal oxide was reduced to obtain the target materials. This metal-support combination was a winning strategy to optimize the hydrogenation properties of Ni to make it suitable for light olefins production via PFT synthesis, performed at 1.8 bar and irradiation with a 300 W Xe light (200-800 nm) for 1 hour, without external heating.…”

Recent advances in VOCs and CO removal via photothermal synergistic catalysis

“…Zhang and coworkers [146] reported a Ni-loaded MnO support for photothermal synergistic catalytic FTS to light olefins under UV-vis irradiation. When the reduction temperature was 500 °C, the prepared catalyst had high activity, and the percentage conversion of CO was 14.9% and the olefin selectivity was 33%.…”

A core-shell catalyst design boosts the performance of photothermal reverse water gas shift catalysis

“…For example, CO can be transformed into different liquid fuels (diesel, gasoline, and alcohols) through further hydrogenation [17,18]. Compared with direct hydrogenation of CO 2 to produce value-added methanol, the CO hydrogenation process is more thermodynamically favorable to achieve a much higher yield [19][20][21]. Through the endothermic RWGS reaction, solar energy is transformed into chemical energy with the ease of large-scale storage and transportation [22,23].…”