Catalytic transformations of syngas (a mixture of H2 and CO), which is one of the most important C1-chemistry platforms, and CO2, a greenhouse gas released from human industrial activities but also a candidate of abundant carbon feedstock, into chemicals and fuels have attracted much attention in recent years. Fischer-Tropsch (FT) synthesis is a classic route of syngas chemistry, but the product selectivity of FT synthesis is limited by the Anderson-Schulz-Flory (ASF) distribution. The hydrogenation of CO2 into C2+ hydrocarbons involving C-C bond formation encounters similar selectivity limitation. The present article focuses on recent advances in breaking the selectivity limitation by using a reaction coupling strategy for hydrogenation of both CO and CO2 into C2+ hydrocarbons, which include key building-block chemicals, such as lower (C2-C4) olefins and aromatics, and liquid fuels, such as gasoline (C5-C11 hydrocarbons), jet fuel (C8-C16 hydrocarbons) and diesel fuel (C10-C20 hydrocarbons). The design and development of novel bifunctional or multifunctional catalysts, which are composed of metal, metal carbide or metal oxide nanoparticles and zeolites, for hydrogenation of CO and CO2 to C2+ hydrocarbons beyond FT synthesis will be reviewed. The key factors in controlling catalytic performances, such as the catalyst component, the acidity and mesoporosity of the zeolite and the proximity between the metal/metal carbide/metal oxide and zeolite, will be analysed to provide insights for designing efficient bifunctional or multifunctional catalysts. The reaction mechanism, in particular the activation of CO and CO2, the reaction pathway and the reaction intermediate, will be discussed to provide a deep understanding of the chemistry of the new C1 chemistry routes beyond FT synthesis.

New horizon in C1 chemistry: breaking the selectivity limitation in transformation of syngas and hydrogenation of CO2 into hydrocarbon chemicals and fuels

Methane undergoes highly facile C–H bond cleavage on the stoichiometric IrO2(110) surface. From temperature-programmed reaction spectroscopy experiments, we found that methane molecularly adsorbed as a strongly bound σ complex on IrO2(110) and that a large fraction of the adsorbed complexes underwent C–H bond cleavage at temperatures as low as 150 kelvin (K). The initial dissociation probability of methane on IrO2(110) decreased from 80 to 20% with increasing surface temperature from 175 to 300 K. We estimate that the activation energy for methane C–H bond cleavage is 9.5 kilojoule per mole (kJ/mol) lower than the binding energy of the adsorbed precursor on IrO2(110), and equal to a value of ~28.5 kJ/mol. Low-temperature activation may avoid unwanted side reactions in the development of catalytic processes to selectively convert methane to value-added products.

https://science.sciencemag.org/content/sci/356/6335/299.full.pdf

Low-temperature activation of methane on the IrO2(110) surface.

Compared to modern fossil-fuel-based refineries, the emerging electrocatalytic refinery (e-refinery) is a more sustainable and environmentally benign strategy to convert renewable feedstocks and energy sources into transportable fuels and value-added chemicals. A crucial step in conducting e-refinery processes is the development of appropriate reactions and optimal electrocatalysts for efficient cleavage and formation of chemical bonds. However, compared to well-studied primary reactions (e.g., O2 reduction, water splitting), the mechanistic aspects and materials design for emerging complex reactions are yet to be settled. To address this challenge, herein, we first present fundamentals of heterogeneous electrocatalysis and some primary reactions, and then implement these to establish the framework of e-refinery by coupling in situ generated intermediates (integrated reactions) or products (tandem reactions). We also present a set of materials design principles and strategies to efficiently manipulate the reaction intermediates and pathways.

Electrocatalytic Refinery for Sustainable Production of Fuels and Chemicals

The reactive oxidizing species in the selective oxidation of methane to methanol in oxygen activated Cu-ZSM-5 was recently defined to be a bent mono(μ-oxo)dicopper(II) species, [Cu(2)O](2+). In this communication we report the formation of an O(2)-precursor of this reactive site with an associated absorption band at 29,000 cm(-1). Laser excitation into this absorption feature yields a resonance Raman (rR) spectrum characterized by (18)O(2) isotope sensitive and insensitive vibrations, νO-O and νCu-Cu, at 736 (Δ(18)O(2) = 41 cm(-1)) and 269 cm(-1), respectively. These define the precursor to be a μ-(η(2):η(2)) peroxo dicopper(II) species, [Cu(2)(O(2))](2+). rR experiments in combination with UV-vis absorption data show that this [Cu(2)(O(2))](2+) species transforms directly into the [Cu(2)O](2+) reactive site. Spectator Cu(+) sites in the zeolite ion-exchange sites provide the two electrons required to break the peroxo bond in the precursor. O(2)-TPD experiments with (18)O(2) show the incorporation of the second (18)O atom into the zeolite lattice in the transformation of [Cu(2)(O(2))](2+) into [Cu(2)O](2+). This study defines the mechanism of oxo-active site formation in Cu-ZSM-5.

Oxygen precursor to the reactive intermediate in methanol synthesis by Cu-ZSM-5

This article describes the main strategies to activate and convert carbon dioxide (CO2) into valuable chemicals over catalytic surfaces. Coherent elements such as common intermediates are identified in the different strategies and concisely discussed based on the reactivity of CO2 with the aim to understand the decisive factors for selective and efficient CO2 conversion.

CO2 Activation over Catalytic Surfaces

Natural gas is envisioned as a primary source of energy and hydrocarbons in the foreseeable future. Though shale gas has recently become abundant, it has two main concerns: its environmental impact and sustainable utilization. The former is the result of recent reports of natural gas emissions and flares into the environment, where it acts as a powerful greenhouse gas, whereas the latter is dictated by the need for efficient hydrocarbon utilization. Modern natural gas processing units that yield clean fuels and feedstock from methane, CH 4 , require extremely large capital investments and are not economical in remote natural gas extraction sites. Single step (direct), non-syngas based catalytic routes of CH 4 conversion to value added products have not been competitive economically and need to be reevaluated in the light of shale gas availability. This perspective discusses general considerations for the desired hydrocarbon products, the thermodynamic limitations involved in a single step conversion of CH 4 and heterogeneous catalytic routes based on high temperatures and oxide based catalysts. We then discuss other catalysts and methods of CH 4 activation that have recently emerged and are conceptually different from metal oxide catalyst based routes, such as those using sulfur or halogens. Lastly, we discuss a possible route of CH 4 monetization beyond the first reactive product (such as ethylene oligomerization into fuels), as well as currently explored photo(electro)chemical routes of CH 4 activation.

CH4 conversion to value added products: Potential, limitations and extensions of a single step heterogeneous catalysis

Surface chemistry of carbon dioxide revisited

Catalytic conversion of ethanol to 1,3-butadiene on MgO: A comprehensive mechanism elucidation using DFT calculations

Surface chemistry of MgO/SiO2 catalyst during the ethanol catalytic conversion to 1,3-butadiene: in-situ DRIFTS and DFT study

The electronic structure and reactivity of Cu- and Zn-promoted wet-kneaded MgO/SiO2 catalysts was interrogated during ethanol reaction to 1,3-BD. A multimodal nature of characterization, including in situ or operando X-ray, electron, light spectroscopies, and steady state reactivity measurements demonstrated critical information on the temporal evolution of the catalyst active sites including key measurements performed in operando conditions using synchrotron techniques (EXAFS and XANES). In situ DRIFT spectroscopy allowed decoupling of the aldol condensation and dehydrogenation reactive steps due to the promotion with enhanced ability to carry out aldol condensation, as correlated with the steady state reactivity experiments. In situ UV–vis spectroscopy presented a complex picture of the adsorbates with π–π* electronic transitions due to the allylic cations, cyclic or aromatic species while also suggesting oligomeric CuO species were formed. Operando X-ray measurements combined with ab initio multiple sc...

William Taifan

Papers

CH4 conversion to value added products: Potential, limitations and extensions of a single step heterogeneous catalysis

Surface chemistry of carbon dioxide revisited

Catalytic conversion of ethanol to 1,3-butadiene on MgO: A comprehensive mechanism elucidation using DFT calculations

Surface chemistry of MgO/SiO2 catalyst during the ethanol catalytic conversion to 1,3-butadiene: in-situ DRIFTS and DFT study

Operando Structure Determination of Cu and Zn on Supported MgO/SiO2 Catalysts during Ethanol Conversion to 1,3-Butadiene