Catalytic Hybrid Electrocatalytic/Biocatalytic Cascades for Carbon Dioxide Reduction and Valorization

Development of Multifunctional Catalysts for the Direct Hydrogenation of Carbon Dioxide to Higher Alcohols

The direct hydrogenation of greenhouse gas CO2 to higher alcohols (C2+OH) provides a new route for the production of high-value chemicals. Due to the difficulty of C-C coupling, the formation of higher alcohols is more difficult compared to that of other compounds. In this review, we summarize recent advances in the development of multifunctional catalysts, including noble metal catalysts, Co-based catalysts, Cu-based catalysts, Fe-based catalysts, and tandem catalysts for the direct hydrogenation of CO2 to higher alcohols. Possible reaction mechanisms are discussed based on the structure-activity relationship of the catalysts. The reaction-coupling strategy holds great potential to regulate the reaction network. The effects of the reaction conditions on CO2 hydrogenation are also analyzed. Finally, we discuss the challenges and potential opportunities for the further development of direct CO2 hydrogenation to higher alcohols.

Biocatalysis of CO2 and CH4: Key enzymes and challenges

Mitigating greenhouse gas emissions is a critical challenge for promoting global sustainability. The utilization of CO2 and CH4 as substrates for the production of valuable products offers a promising avenue for establishing an eco-friendly economy. Biocatalysis, a sustainable process utilizing enzymes to facilitate biochemical reactions, plays a significant role in upcycling greenhouse gases. This review provides a comprehensive overview of the enzymes and associated reactions involved in the biocatalytic conversion of CO2 and CH4. Furthermore, the challenges facing the field are discussed, paving the way for future research directions focused on developing robust enzymes and systems for the efficient fixation of CO2 and CH4.

Direct Biocatalytic Processes for CO2 Capture as a Green Tool to Produce Value-Added Chemicals

Direct biocatalytic processes for CO₂ capture and transformation in value-added chemicals may be considered a useful tool for reducing the concentration of this greenhouse gas in the atmosphere. Among the other enzymes, carbonic anhydrase (CA) and formate dehydrogenase (FDH) are two key biocatalysts suitable for this challenge, facilitating the uptake of carbon dioxide from the atmosphere in complementary ways. Carbonic anhydrases accelerate CO₂ uptake by promoting its solubility in water in the form of hydrogen carbonate as the first step in converting the gas into a species widely used in carbon capture storage and its utilization processes (CCSU), particularly in carbonation and mineralization methods. On the other hand, formate dehydrogenases represent the biocatalytic machinery evolved by certain organisms to convert CO₂ into enriched, reduced, and easily transportable hydrogen species, such as formic acid, via enzymatic cascade systems that obtain energy from chemical species, electrochemical sources, or light. Formic acid is the basis for fixing C₁-carbon species to other, more reduced molecules. In this review, the state-of-the-art of both methods of CO₂ uptake is assessed, highlighting the biotechnological approaches that have been developed using both enzymes.

Alternative design strategies to help build the enzymatic retrosynthesis toolbox

Most of the complex molecules found in nature still cannot be synthesized by current organic chemistry methods. Given the number of enzymes that exist in nature and the incredible potential of directed evolution, the field of synthetic biology contains perhaps all the necessary building blocks to bring about the realization of applied enzymatic retrosynthesis. Current thinking anticipates that enzymatic retrosynthesis will be implemented using conventional cell-based synthetic biology approaches where requisite native, heterologous, designer, and evolved enzymes making up a given multi-enzyme pathway are hosted by chassis organisms to carry out designer synthesis. In this perspective, we suggest that such an effort should not be limited by solely exploiting living cells and enzyme evolution and describe some useful yet less intensive complementary approaches that may prove especially productive in this grand scheme. By decoupling reactions from the environment of a living cell, a significantly larger portion of potential synthetic chemical space becomes available for exploration; most of this area is currently unavailable to cell-based approaches due to toxicity issues. In contrast, in a cell-free reaction a variety of classical enzymatic approaches can be exploited to improve performance and explore and understand a given enzyme's substrate specificity and catalytic profile towards non-natural substrates. We expect these studies will reveal unique enzymatic capabilities that are not accessible in living cells.

Novel and sustainable carboxylation of terminal alkynes and CO2 to alkynyl carboxylic acids using triazolium ionic liquid-modified PMO-supported transition metal acetylacetonate as effective cooperative catalysts

Efficient and sustainable chemical fixation of CO₂ into value-added chemicals is one of the most promising objectives in environmental chemistry. In this work, transition metal acetylacetonate immobilized onto triazolium ionic liquid-modified periodic mesoporous organosilica PMO-IL-M(x) was successfully prepared and investigated as an effective and heterogeneous catalyst in the direct carboxylation of terminal alkynes and CO₂ to the desired alkynyl carboxylic acids. It was found that the catalyst PMO-IL-Sn(0.3) exhibited extraordinary catalytic performance in terms of excellent activity, stability, productivity, and excellent yields under mild reaction conditions. Moreover, the catalyst PMO-IL-Sn(0.3) could be easily recovered and reused at least six times without considerable loss in catalytic activity. This work provides a sustainable and efficient synergistic strategy for the chemical fixation of carbon dioxide into valuable alkynyl carboxylic acids.

Photosynthesis of Acetate by Sporomusa ovata-CdS Biohybrid System

Sporomusa ovata, a typical electroautotrophic microorganism, has been utilized in bioelectrosynthesis for carbon dioxide fixation to multicarbon organic chemicals. However, additional photovoltaic devices are normally needed to convert photo energy to electric energy to power the carbon dioxide fixation, which restricts the overall energy conversion efficiency. Herein, we report Sporomusa ovata-CdS biohybrids for artificial photosynthesis driven by light without any other power source. The quantum yield can reach 16.8 ± 9%, and the active duration time of the system can last for 5 days. During the artificial photosynthesis, carbon dioxide is first reduced to formate and finally converted to acetate via the Wood-Ljungdahl pathway. The carbon dioxide fixation, electron transfer, energy metabolism, and reactive oxygen species damage repair processes in the biohybrid system were characterized by proteomic analysis. Key enzymes, e.g., flavoprotein, ferredoxin, formate-tetrahydrofolate ligase, 5-methyltetrahydrofolate:corrinoid iron-sulfur protein methyltransferase, thioredoxin, and rubrerythrin, were found up-regulated in the biohybrid system. The findings are helpful in understanding the mechanism of the artificial photosynthesis and useful for the development of new biohybrid systems using genetically engineered microbes in the future. The study is expected to boost the development of bioabiotic hybrid system in solar energy harvest.

Catalysis for e-Chemistry: Need and Gaps for a Future De-Fossilized Chemical Production, with Focus on the Role of Complex (Direct) Syntheses by Electrocatalysis

The prospects, needs and limits in current approaches in catalysis to accelerate the transition to e-chemistry, where this term indicates a fossil fuel-free chemical production, are discussed. It is suggested that e-chemistry is a necessary element of the transformation to meet the targets of net zero emissions by year 2050 and that this conversion from the current petrochemistry is feasible. However, the acceleration of the development of catalytic technologies based on the use of renewable energy sources (indicated as reactive catalysis) is necessary, evidencing that these are part of a system of changes and thus should be assessed from this perspective. However, it is perceived that the current studies in the area are not properly addressing the needs to develop the catalytic technologies required for e-chemistry, presenting a series of relevant aspects and directions in which research should be focused to develop the framework system transformation necessary to implement e-chemistry.

Engineering formaldehyde dehydrogenase from Pseudomonas putida to favor nicotinamide cytosine dinucleotide

The enzyme formaldehyde dehydrogenase (FalDH) from Pseudomonas putida is of particular interest for biotechnological applications as it catalyses the oxidation of formaldehyde independent of glutathione. However, the consumption of a stoichiometric amount of nicotinamide adenine dinucleotide (NAD) can be challenging at the metabolic level as this may affect many other NAD-linked processes. A potential solution is to engineer FalDH to utilize non-natural cofactors. Here we devised FalDH variants to favor nicotinamide cytosine dinucleotide (NCD) by structure-guided modification of the binding pocket for the adenine moiety of NAD. Several mutants were obtained and the best one FalDH 9B2 had over 150-fold higher preference for NCD than NAD. Molecular docking analysis indicated that the cofactor binding pocket shrinked to better fit NCD, a smaller-sized cofactor. FalDH 9B2 together with other NCD-linked enzymes offer opportunities to assemble orthogonal pathways for biological conversion of C1 molecules.

Advances in Palladium-Catalyzed Carboxylation Reactions

In this short review, we highlight the advancements in the field of palladium-catalyzed carbon dioxide utilization for the synthesis of high value added organic molecules. The review is structured on the basis of the kind of substrate undergoing the Pd-catalyzed carboxylation process. Accordingly, after the introductory section, the main sections of the review will illustrate Pd-catalyzed carboxylation of olefinic substrates, acetylenic substrates, and other substrates (aryl halides and triflates).

Multiple electron transfer pathways of tungsten-containing formate dehydrogenase in direct electron transfer-type bioelectrocatalysis

Tungsten-containing formate dehydrogenase from Methylorubrum extroquens AM1 (FoDH1)—a promising biocatalyst for the interconversion of carbon dioxide/formate and nicotine adenine dinucleotide (NAD+)/NADH redox couples—was investigated from structural biology and bioelectrochemistry. FoDH1...

Predicting the Conformation of Organic Catalysts Grafted on Silica Surfaces with Different Numbers of Tethering Chains: The Silicopodality Concept

Hybrid catalysts are attracting much attention, since they combine the versatility and efficiency of homogeneous organic catalysis with the robustness and thermal stability of solid materials, for example, mesoporous silica; in addition, they can be used in cascade reactions, for exploring both organic and inorganic catalysis at the same time. Despite the importance of the organic/inorganic interface in these materials, the effect of the grafting architecture on the final conformation of the organic layer (and hence its reactivity) is still largely unexplored. Here, we investigate a series of organosiloxanes comprising a pyridine ring (the catalyst model) and different numbers of alkylsiloxane chains used to anchor it to the MCM-41 surface. The hybrid interfaces are characterized with X-ray powder diffraction, thermogravimetric analyses, Fourier-transform infrared spectroscopy, nuclear magnetic resonance techniques and are modeled theoretically through molecular dynamics (MD) simulations, to determine the relationship between the number of chains and the average position of the pyridine group; MD simulations also provide some insights about temperature and solvent effects.