Owing to the increasing emissions of carbon dioxide (CO2), human life and the ecological environment have been affected by global warming and climate changes. To mitigate the concentration of CO2 in the atmosphere various strategies have been implemented such as separation, storage, and utilization of CO2. Although it has been explored for many years, hydrogenation reaction, an important representative among chemical conversions of CO2, offers challenging opportunities for sustainable development in energy and the environment. Indeed, the hydrogenation of CO2 not only reduces the increasing CO2 buildup but also produces fuels and chemicals. In this critical review we discuss recent developments in this area, with emphases on catalytic reactivity, reactor innovation, and reaction mechanism. We also provide an overview regarding the challenges and opportunities for future research in the field (319 references).

Recent advances in catalytic hydrogenation of carbon dioxide

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Studies in Surface Science and Catalysis

Replacement of part of the fossil fuel consumption by renewable energy, in particular in the chemical industry, is a central strategy for resource and energy efficiency. This perspective will show that CO2 is the key molecule to proceed effectively in this direction. The routes, opportunities and barriers in increasing the share of renewable energy by using CO2 reaction and their impact on the chemical and energy value chains are discussed after introducing the general aspects of this topic evidencing the tight integration between the CO2 use and renewable energy insertion in the value chain of the process industry. The focus of this perspective article is on the catalytic aspects of the chemistries involved, with an analysis of the state-of-the-art, perspectives and targets to be developed. The reactions discussed are the production of short-chain olefins (ethylene, propylene) from CO2, and the conversion of carbon dioxide to syngas, formic acid, methanol and dimethyl ether, hydrocarbons via Fischer–Tropsch synthesis and methane. The relevance of availability, cost and environmental footprints of H2 production routes using renewable energies is addressed. The final part discusses the possible scenario for CO2 as an intermediary for the incorporation of renewable energy in the process industry, with a concise roadmap for catalysis needs and barriers to reach this goal.

Catalysis for CO2 conversion: a key technology for rapid introduction of renewable energy in the value chain of chemical industries

Ocean acidification and climate change are expected to be two of the most difficult scientific challenges of the 21st century. Converting CO2 into valuable chemicals and fuels is one of the most practical routes for reducing CO2 emissions while fossil fuels continue to dominate the energy sector. Reducing CO2 by H2 using heterogeneous catalysis has been studied extensively, but there are still significant challenges in developing active, selective and stable catalysts suitable for large-scale commercialization. The catalytic reduction of CO2 by H2 can lead to the formation of three types of products: CO through the reverse water–gas shift (RWGS) reaction, methanol via selective hydrogenation, and hydrocarbons through combination of CO2 reduction with Fischer–Tropsch (FT) reactions. Investigations into these routes reveal that the stabilization of key reaction intermediates is critically important for controlling catalytic selectivity. Furthermore, viability of these processes is contingent on the development of a CO2-free H2 source on a large enough scale to significantly reduce CO2 emissions.

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Catalytic reduction of CO2 by H2 for synthesis of CO, methanol and hydrocarbons: challenges and opportunities

Fossil fuel depletion, global warming, climate change, and steep hikes in the price of fuels are driving scientists to investigate on commercial and environmentally friendly fuels. The process of CO2 conversion to value-added products has been considered as a possible remedy to fulfill the requirements. The present review paper comprehensively discusses two different processes, namely hydrocarbon and methanol synthesis which are extensively used to convert CO2 to value-added products. Reaction mechanisms as well as the effects of catalyst, reactor type and operating conditions on product efficiency enhancement of each process are reviewed. Furthermore a brief overview on the reactor types as the most effective component of the theoretical and experimental reported results on the process improvement is given. All the information is tabulated in order to make the gathered information easily conclusive. Finally, by taking the available information into account the best reactor configuration which is adjustable to reaction mechanism is proposed.

Hydrogenation of CO2 to value-added products—A review and potential future developments

Kinetics of Fischer–Tropsch synthesis on titania-supported cobalt

Hydrogenation of CO, CO 2 and their mixtures has been comparatively studied in this work on a representative cobalt-based catalyst under typical Fischer–Tropsch synthesis conditions ( T  = 220 °C, P  = 20 bar, GHSV = 4800 cm 3 (STP)/h/g cat , H 2 /CO x  = 2.45–4.9 mol/mol). In addition, the interactions of the adopted catalyst with CO, CO 2 and their mixtures have been studied by FT-IR spectroscopy. When used alone, both CO and CO 2 are easily hydrogenated over the adopted catalyst, with CO 2 showing a reactivity higher then CO. However the selectivity of the two processes is extremely different, with over 90% of the products represented by methane in the case of CO 2 hydrogenation. No evidence has been found for the involvement of different surface species in CO and CO 2 hydrogenation, suggesting that the observed reaction products originate from the same intermediate. It is speculated that the different reactivity of the mixtures CO/H 2 and CO 2 /H 2 is due to the different adsorption ability of CO and CO 2 , which strongly affects the H/C atomic ratio on the catalyst surface. The higher H/C ratio resulting upon CO 2 hydrogenation inhibits the chain growth, hence favoring the methanation reaction. In the presence of CO, CO 2 is hardly hydrogenated and behaves as an inert species: this has been ascribed to a competition between CO and CO 2 for the adsorption on the catalyst active sites.

Fischer–Tropsch synthesis on a Co/Al2O3 catalyst with CO2 containing syngas

http://nacatsoc.org/20nam/abstracts/P-S6-07C.pdf

Development of a complete kinetic model for the Fischer-Tropsch synthesis over Co/Al2O3 catalysts

The objective of this work was to obtain kinetic data on a well-characterized, titania-supported catalyst under commercially-representative reaction conditions. Effects of water partial pressure on the activity of Co/titania were also considered.

Roberto Zennaro

Papers

Kinetics of Fischer–Tropsch synthesis on titania-supported cobalt

Fischer–Tropsch synthesis on a Co/Al2O3 catalyst with CO2 containing syngas

Development of a complete kinetic model for the Fischer-Tropsch synthesis over Co/Al2O3 catalysts

Kinetics of Fischer-Tropsch synthesis on titania-supported cobalt

Monolithic catalysts with high thermal conductivity for the Fischer–Tropsch synthesis in tubular reactors