Efficient Synthesis of Ethanol from CH4 and Syngas on a Cu-Co/TiO2 Catalyst Using a Stepwise Reactor

Theoretical insight into the electrocatalytic reduction of CO2 with different metal ratios and reaction mechanisms on palladium-copper alloys

Environmental impacts of continued CO2 production have led to an increased need for new methods of CO2 removal and energy development. Electrochemical reduction of CO2 has been shown to be a good method through recent studies. Alloys are of special interest for these applications, because of their unique chemical and physical properties that allow for highly active surfaces. Here, PdnCum (m + n = 15 and n > m) bimetallic electrocatalysts were used for systematic studies to understand the effect of the composition of Pd and Cu on the electrochemical reduction of CO2 to CO. In particular, the Pd-Cu alloy with the Pd/Cu = 2/1 atomic ratio (i.e., Pd10Cu5) has the best catalytic effect, particularly true at the step of the hydrogenation of CO2 to COOH, and the Pd10Cu5 catalyst is better than most known electrodes. With the energetic analysis of the proposed reaction pathways over the Pd10Cu5 catalyst, the limiting voltages for CO2 reduction to CH3OH, CH4, and CH3CH2O have been compared. Most importantly, the kinetic model analysis showed that the rate constant values indicate that the probability of generating C2H5OH on the Pd10Cu5 catalyst is greater than that of CH3OH or CH4. The findings revealed in this study may shed some light on the design of cost-effective and efficient electrocatalysts for CO2 conversion to CO or to other useful hydrocarbons.

CO oxidative coupling to dimethyl oxalate over Pd-Me (Me = Cu, Al) catalysts: a combined DFT and kinetic study

CO oxidative coupling to dimethyl oxalate (DMO) on Pd(111), Pd-Cu(111) and Pd-Al(111) surfaces was systematically investigated by means of density functional theory (DFT) together with periodic slab models and micro-kinetic modeling. The binding energy results show that Cu and Al can be fine substrates to stably support Pd. The favorable pathway for DMO synthesis on these catalysts starts from the formation of two COOCH₃ intermediates, followed by the coupling to each other, and the catalytic activity follows the trend of Pd-Al(111) > Pd(111) > Pd-Cu(111). Additionally, the formation of DMO is far favorable than that of dimethyl carbonate (DMC) on these catalysts. The results were further demonstrated by micro-kinetic modeling. Therefore, Pd-Al bimetallic catalysts can be applied in practice to effectively enhance the catalytic performance and greatly reduce the cost. This study can help with fine-tuning and designing of high-efficient and low-cost Pd-based bimetallic catalysts.

A short review of recent advances in CO2 hydrogenation to hydrocarbons over heterogeneous catalysts

CO2 hydrogenation to hydrocarbons is a promising way of making waste to wealth and energy storage, which also solves the environmental and energy issues caused by CO2 emissions. Much efforts and research are aimed at the conversion of CO2 via hydrogenation to various value-added hydrocarbons, such as CH4, lower olefins, gasoline, or long-chain hydrocarbons catalyzed by different catalysts with various mechanisms. This review provides an overview of advances in CO2 hydrogenation to hydrocarbons that have been achieved recently in terms of catalyst design, catalytic performance and reaction mechanism from both experiments and density functional theory calculations. In addition, the factors influencing the performance of catalysts and the first C-C coupling mechanism through different routes are also revealed. The fundamental factor for product selectivity is the surface H/C ratio adjusted by active metals, supports and promoters. Furthermore, the technical and application challenges of CO2 conversion into useful fuels/chemicals are also summarized. To meet these challenges, future research directions are proposed in this review.

Evidence of a strong effect of defect-free metal oxide supports on Pt nanoparticles

Influence of metal oxide (MO) supports on nanoparticle (NP) catalysts is still under investigation. Theoretical studies demonstrate that active defect sites on the surface of a MO support can affect the structure and activity of metal clusters. In the present work, we show that even defect-free surfaces of MOs can cause considerable restructuring and accumulation of interfacial charges on Pt NPs of size 1 nm (Pt₅₅). Independent of the type of MO support, we find that supported Pt₅₅ behaves like a conductor since the binding energy of a test adsorbate on top of it is similar to that on an intact Pt₅₅. However, adsorption energy at binding sites close to the perimeter of the nanoparticle/support interface can vary by 1.8 eV depending on the distance between the adsorbate and surface cations (possibility of forming ionic bonds) as well as the amount and sign of charges (ionization energy) of interfacial Pt atoms.