CO2 hydrogenation to light olefins over Cu-CeO2/SAPO-34 catalysts: Product distribution and optimization

Selectivity control by zeolites during methanol-mediated CO2 hydrogenation processes

The thermocatalytic conversion of CO2 with green or blue hydrogen into valuable energy and commodity chemicals such as alcohols, olefins, and aromatics emerges as one of the most promising strategies for mitigating global warming concerns in the future. This process can follow either a CO2-modified Fischer-Tropsch synthesis route or a methanol-mediated route, with the latter being favored for its high product selectivity beyond the Anderson-Schulz-Flory distribution. Despite the progress of the CO2-led methanol-mediated route over bifunctional metal/zeolite catalysts, challenges persist in developing catalysts with both high activity and selectivity due to the complexity of CO2 hydrogenation reaction networks and the difficulty in controlling C-O bond activation and C-C bond coupling on multiple active sites within zeolites. Moreover, the different construction and proximity modes of bifunctionality involving redox-based metallic sites and acidic zeolite sites have been explored, which have not been systematically reviewed to derive reliable structure-reactivity relationships. To bridge this "knowledge gap", in this review, we will provide a comprehensive and critical overview of contemporary research on zeolite-confined metal catalysts for alcohol synthesis and zeolite-based bifunctional tandem/cascade catalytic systems for C2+ hydrocarbons synthesis in CO2 hydrogenation via the methanol-mediated route. Accordingly, special emphasis will be placed on evaluating how confinement and proximity effects within the "redox-acid" bifunctional systems influence the reaction outcomes, particularly regarding product selectivity, which has also been analyzed from the mechanistic standpoint. This review will also examine the synergistic interactions among various catalyst components that govern catalysis, offering valuable insights for the rational design of new or improved catalyst systems. By discussing current challenges and recognizing future opportunities in CO2 hydrogenation using zeolite-based bifunctional catalysis, this review aims to contribute to the advancement of sustainable and efficient processes for CO2 valorization.

A Review on Green Hydrogen Valorization by Heterogeneous Catalytic Hydrogenation of Captured CO2 into Value-Added Products

The catalytic hydrogenation of captured CO2 by different industrial processes allows obtaining liquid biofuels and some chemical products that not only present the interest of being obtained from a very low-cost raw material (CO2) that indeed constitutes an environmental pollution problem but also constitute an energy vector, which can facilitate the storage and transport of very diverse renewable energies. Thus, the combined use of green H2 and captured CO2 to obtain chemical products and biofuels has become attractive for different processes such as power-to-liquids (P2L) and power-to-gas (P2G), which use any renewable power to convert carbon dioxide and water into value-added, synthetic renewable E-fuels and renewable platform molecules, also contributing in an important way to CO2 mitigation. In this regard, there has been an extraordinary increase in the study of supported metal catalysts capable of converting CO2 into synthetic natural gas, according to the Sabatier reaction, or in dimethyl ether, as in power-to-gas processes, as well as in liquid hydrocarbons by the Fischer-Tropsch process, and especially in producing methanol by P2L processes. As a result, the current review aims to provide an overall picture of the most recent research, focusing on the last five years, when research in this field has increased dramatically.

Light olefin synthesis from a diversity of renewable and fossil feedstocks: state-of the-art and outlook

Light olefins are important feedstocks and platform molecules for the chemical industry. Their synthesis has been a research priority in both academia and industry. There are many different approaches to the synthesis of these compounds, which differ by the choice of raw materials, catalysts and reaction conditions. The goals of this review are to highlight the most recent trends in light olefin synthesis and to perform a comparative analysis of different synthetic routes using several quantitative characteristics: selectivity, productivity, severity of operating conditions, stability, technological maturity and sustainability. Traditionally, on an industrial scale, the cracking of oil fractions has been used to produce light olefins. Methanol-to-olefins, alkane direct or oxidative dehydrogenation technologies have great potential in the short term and have already reached scientific and technological maturities. Major progress should be made in the field of methanol-mediated CO and CO₂ direct hydrogenation to light olefins. The electrocatalytic reduction of CO₂ to light olefins is a very attractive process in the long run due to the low reaction temperature and possible use of sustainable electricity. The application of modern concepts such as electricity-driven process intensification, looping, CO₂ management and nanoscale catalyst design should lead in the near future to more environmentally friendly, energy efficient and selective large-scale technologies for light olefin synthesis.

Modified fischer-tropsch synthesis: A review of highly selective catalysts for yielding olefins and higher hydrocarbons

Global warming, fossil fuel depletion, climate change, as well as a sudden increase in fuel price have motivated scientists to search for methods of storage and reduction of greenhouse gases, especially CO2. Therefore, the conversion of CO2 by hydrogenation into higher hydrocarbons through the modified Fischer–Tropsch Synthesis (FTS) has become an important topic of current research and will be discussed in this review. In this process, CO2 is converted into carbon monoxide by the reverse water-gas-shift reaction, which subsequently follows the regular FTS pathway for hydrocarbon formation. Generally, the nature of the catalyst is the main factor significantly influencing product selectivity and activity. Thus, a detailed discussion will focus on recent developments in Fe-based, Co-based, and bimetallic catalysts in this review. Moreover, the effects of adding promoters such as K, Na, or Mn on the performance of catalysts concerning the selectivity of olefins and higher hydrocarbons are assessed.

Hydrogenation of CO2 on Nanostructured Cu/FeOx Catalysts: The Effect of Morphology and Cu Load on Selectivity

The aim of this work was to study the influence of copper content and particle morphology on the performance of Cu/FeOx catalysts in the gas-phase conversion of CO2 with hydrogen. All four investigated catalysts with a copper content between 0 and 5 wt% were found highly efficient, with CO2 conversion reaching 36.8%, and their selectivity towards C1 versus C2-C4, C2-C4=, and C5+ products was dependent on catalyst composition, morphology, and temperature. The observed range of products is different from those observed for catalysts with similar composition but synthesized using other precursors and chemistries, which yield different morphologies. The findings presented in this paper indicate potential new ways of tuning the morphology and composition of iron-oxide-based particles, ultimately yielding catalyst compositions and morphologies with variable catalytic performances.

A Review on SAPO-34 Zeolite Materials for CO2 Capture and Conversion

Among several known zeolites, silicoaluminophosphate (SAPO)-34 zeolite exhibits a distinct chemical structure, unique pore size distribution, and chemical, thermal, and ion exchange capabilities, which have recently attracted considerable research attention. Global carbon dioxide (CO₂ ) emissions are a serious environmental issue. Current atmospheric CO₂ level exceeds 414 parts per million (ppm), which greatly influences humans, fauna, flora, and the ecosystem as a whole. Zeolites play a vital role in CO₂ removal, recycling, and utilization. This review summarizes the properties of the SAPO-34 zeolite and its role in CO₂ capture and separation from air and natural gas. In addition, due to their high thermal stability and catalytic nature, CO₂ conversions into valuable products over single metal, bi-metallic, and tri-metallic catalysts and their oxides supported on SAPO-34 were also summarized. Considering these accomplishments, substantial problems related to SAPO-34 are discussed, and future recommendations are offered in detail to predict how SAPO-34 could be employed for greenhouse gas mitigation.

Carbon Nanotube/Pt Cathode Nanocomposite Electrode in Microbial Fuel Cells for Wastewater Treatment and Bioenergy Production

In this paper, we reported the fabrication, characterization, and application of carbon nanotube (CNT)-platinum nanocomposite as a novel generation of cathode catalyst in microbial fuel cells (MFCs) for sustainable energy production and wastewater treatment. The efficiency of the carbon nanocomposites was compared by platinum (Pt), which is the most effective and common cathode catalyst. This nanocomposite is utilized to benefit from the catalytic properties of CNTs and reduce the amount of required Pt, as it is an expensive catalyst. The CNT/Pt nanocomposites were synthesized via a chemical reduction technique and the electrodes were characterized by field emission scanning electron microscopy, electronic dispersive X-Ray analysis, and transmission electron microscopy. The nanocomposites were applied as cathode catalysts in the MFC to obtain polarization curve and coulombic efficiency (CE) results. The catalytic properties of electrodes were tested by linear sweep voltammetry. The CNT/Pt at the concentration of 0.3 mg/cm2 had the highest performance in terms of CE (47.16%), internal resistance (551 Ω), COD removal (88.9%), and power generation (143 mW/m2). In contrast, for the electrode with 0.5 mg/L of Pt catalyst, CE, internal resistance, COD removal, and power generation were 19%, 810 Ω, 96%, and 84.1 mW/m2, respectively. So, it has been found that carbon nanocomposite cathode electrodes had better performance for sustainable clean energy production and COD removal by MFC.

Recent advances in hydrogenation of CO2 into hydrocarbons via methanol intermediate over heterogeneous catalysts

This review provides recent advances in the conversion of CO₂ to methanol, methanol to hydrocarbons, and direct conversion of CO₂ to hydrocarbons via methanol intermediate over various monofunctional and bifunctional solid catalysts.