Methanol synthesis by CO2 hydrogenation is attractive in view of avoiding the environmental implications associated with the production of the traditional syngas feedstock and mitigating global warming. However, there still is a lack of efficient catalysts for such alternative processes. Herein, we unveil the high activity, 100 % selectivity, and remarkable stability for 1000 h on stream of In2 O3 supported on ZrO2 under industrially relevant conditions. This strongly contrasts to the benchmark Cu-ZnO-Al2 O3 catalyst, which is unselective and experiences rapid deactivation. In-depth characterization of the In2 O3 -based materials points towards a mechanism rooted in the creation and annihilation of oxygen vacancies as active sites, whose amount can be modulated in situ by co-feeding CO and boosted through electronic interactions with the zirconia carrier. These results constitute a promising basis for the design of a prospective technology for sustainable methanol production.

Methanol synthesis by CO 2 hydrogenation is attractive in view of avoiding the environmental implications associated with the production of the traditional syngas feedstocka nd mitigating global warming.H owever,t here still is al acko fe fficient catalysts for such alternative processes. Herein, we unveil the high activity,1 00 %s electivity,a nd remarkable stability for 1000 ho ns tream of In 2 O 3 supported on ZrO 2 under industrially relevant conditions.T his strongly contrasts to the benchmark Cu-ZnO-Al 2 O 3 catalyst, which is unselective and experiences rapid deactivation. In-depth characterization of the In 2 O 3 -based materials points towards am echanism rooted in the creation and annihilation of oxygen vacancies as active sites,w hose amount can be modulated in situ by co-feeding CO and boosted through electronic interactions with the zirconia carrier.T hese results constitute ap romising basis for the design of ap rospective technology for sustainable methanol production.Methanol is akey building block in the chemical industry, [1] with prospects as asustainable energy carrier if its production is accomplished from CO 2 (captured from large-point emitters) and H 2 (retrieved from renewable sources). [2] This application demands novel catalysts as the ternary Cu-ZnO-Al 2 O 3 system currently employed for methanol synthesis from mixed syngas (CO/CO 2 /H 2 )e xhibits limited activity in CO 2 hydrogenation, because of the inhibiting effect of the water byproduct, [3] low selectivity,owing to its significant activity in the parasitic reverse water-gas shift (RWGS) reaction, [4] and insufficient stability,d ue to water-induced sintering of the active phase. [5] Furthermore,t he intricate network of syner-gistic structural and electronic effects between its components hampers the rational optimization of this material. [4a, 6] Among other catalysts studied, [7] only Cu-ZnO-Ga 2 O 3 /SiO 2 and LaCr 0.5 Cu 0.5 O 3 displayed improved methanol formation rates and high selectivities (up to 99.5 %), but their scalability and long-term stability have not been assessed. Recent experiments on Cu/CeO x /TiO 2 model surfaces [8] also showed promising results,but no attempt has been made to translate this material into ap ractically relevant polycrystalline solid.In our quest for as uitable catalyst, we were intrigued by the much simpler In 2 O 3 system. This reducible oxide is commonly used together with SnO 2 as av ery stable conductive transparent layer in organic light-emitting diodes and thin-film transistors. [9] Moreover,i th as demonstrated high activity and selectivity in multiple catalytic transformations involving CO 2 ,i ncluding electrochemical conversion into formic acid, [10] photocatalytic reduction to CO, [11] and methanol steam reforming. [12] Recently,d ensity functional theory (DFT) studies on CO 2 hydrogenation over non-defective [13] and defective [14] In 2 O 3 (110) surfaces suggested that methanol is the most favorable product and that the reaction follows am echanism comprising the cyclic c...

In the last decade, the semi-hydrogenation of alkynes has experienced significant advances in terms of fine control of alkene selectivity and prevention of the over-hydrogenation reaction. Such advances have been possible to a large extent through the progress in colloidal methods for the preparation of metallic nanoparticles. The present review describes the contributions in the field of the selective hydrogenation of alkynes involving the utilization of colloidal methodologies. These approaches permit the fine modulation of several parameters affecting the catalytic performance of the active phase such as the particle size, the bulk and the surface structure and composition. For the transformation of liquid substrates, the nature of the stabilizers, the reducing agents and the metal precursors employed for the synthesis of the catalysts can be tuned to enhance the alkene selectivity. In contrast, in catalytic transformations of gaseous substrates, the presence of adsorbed species at the metal surface usually gives detrimental results while the interplay between the support and the active phase appears to be a more convincing alternative for catalyst tuning.

In this study, we gathered further understanding of the function of the components in the Cu-ZnOAl 2 O 3 catalyst for methanol synthesis from mixed syngas feeds (CO/CO 2 /H 2 ) to rationally develop systems displaying superior performance. In order to unravel the role of ZnO in the hydrogenation of the preferred methanol source, CO 2 , and in the (reverse) water−gas shift ((R)WGS) reaction, we tested coprecipitated materials with variable surface zinc content under industrially relevant conditions (5.0 MPa, 503−543 K). We found that a surface enrichment in zinc leads to higher activity and selectivity due to (i) the enhancement of the unique synergistic Cu-ZnO interactions boosting CO 2 hydrogenation, (ii) the inhibition of the RWGS reaction which produces the undesired CO, and (iii) the electronic stabilization of the Cu sites against reoxidation by CO 2 or H 2 O. Thus, a catalyst with a surface Zn/(Cu + Zn) ratio of 0.8 displayed superior catalytic properties than a commercial benchmark sample, which featured only half of the ratio. An even more performing catalyst was obtained utilizing oxalates instead of hydroxycarbonates as precursors. The better thermal degradation of the former minimizes the content of residual carbon on the surface of the activated catalyst improving the amount of Cu-ZnO contacts. The retention of the metallic state of copper was greatly favored by the deposition of an electron-withdrawing metal such as gold. The Cu-based activity in mixed syngas and CO 2 hydrogenation of the zinc-rich gold-promoted catalyst was ca. 2 and 4 times higher, respectively, than that of the commercial system.

A three-step sintering mechanism is proposed for Co-based catalysts under Fischer–Tropsch reaction conditions. This mechanism includes an intermediate formation of oxide layer on cobalt metal nanoparticles in the presence of water. The partially reversibly oxidized surface accelerates sintering by both reducing the surface energy and enhancing the diffusion rates of cobalt particles. The proposed mechanism is then employed for a fixed-bed unsteady state reactor. The effect of particle growth on the catalytic activity was analyzed within a diverse range of operating conditions (syngas ratio = 1.5–4, water co-feed ratio = 0–6, inert co-feed ratio = 0–6). It is found that, at the same gas space velocity, sintering proceeds faster at higher H2/CO ratios. At the same initial conversion, a low H2/CO syngas ratio increases sintering severity, i.e., catalyst deactivation due to the crystallite growth, as it brings about higher relative water partial pressure. Dilution of syngas with different amounts of inert gas does not affect the cobalt sintering rate. Cobalt sintering proceeds more rapidly if water is co-fed during the reaction.