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

Carbon capture and storage (CCS) is broadly recognised as having the potential to play a key role in meeting climate change targets, delivering low carbon heat and power, decarbonising industry and, more recently, its ability to facilitate the net removal of CO2 from the atmosphere. However, despite this broad consensus and its technical maturity, CCS has not yet been deployed on a scale commensurate with the ambitions articulated a decade ago. Thus, in this paper we review the current state-of-the-art of CO2 capture, transport, utilisation and storage from a multi-scale perspective, moving from the global to molecular scales. In light of the COP21 commitments to limit warming to less than 2 °C, we extend the remit of this study to include the key negative emissions technologies (NETs) of bioenergy with CCS (BECCS), and direct air capture (DAC). Cognisant of the non-technical barriers to deploying CCS, we reflect on recent experience from the UK's CCS commercialisation programme and consider the commercial and political barriers to the large-scale deployment of CCS. In all areas, we focus on identifying and clearly articulating the key research challenges that could usefully be addressed in the coming decade.

/pdf/carbon-capture-and-storage-ccs-the-way-forward-11rgsqyer0.pdf

Carbon capture and storage (CCS): the way forward

This review highlights recent developments and future perspectives in carbon dioxide usage for the sustainable production of energy and chemicals and to reduce global warming. We discuss the heterogeneously catalysed hydrogenation, as well as the photocatalytic and electrocatalytic conversion of CO2 to hydrocarbons or oxygenates. Various sources of hydrogen are also reviewed in terms of their CO2 neutrality. Technologies have been developed for large-scale CO2 hydrogenation to methanol or methane. Their industrial application is, however, limited by the high price of renewable hydrogen and the availability of large-volume sources of pure CO2. With regard to the direct electrocatalytic reduction of CO2 to value-added chemicals, substantial advances in electrodes, electrolyte, and reactor design are still required to permit the development of commercial processes. Therefore, in this review particular attention is paid to (i) the design of metal electrodes to improve their performance and (ii) recent developments of alternative approaches such as the application of ionic liquids as electrolytes and of microorganisms as co-catalysts. The most significant improvements both in catalyst and reactor design are needed for the photocatalytic functionalisation of CO2 to become a viable technology that can help in the usage of CO2 as a feedstock for the production of energy and chemicals. Apart from technological aspects and catalytic performance, we also discuss fundamental strategies for the rational design of materials for effective transformations of CO2 to value-added chemicals with the help of H2, electricity and/or light.

/pdf/status-and-perspectives-of-co2-conversion-into-fuels-and-aitrajygas.pdf

Status and perspectives of CO2 conversion into fuels and chemicals by catalytic, photocatalytic and electrocatalytic processes

CO2 conversion covers a wide range of possible application areas from fuels to bulk and commodity chemicals and even to specialty products with biological activity such as pharmaceuticals. In the present review, we discuss selected examples in these areas in a combined analysis of the state-of-the-art of synthetic methodologies and processes with their life cycle assessment. Thereby, we attempted to assess the potential to reduce the environmental footprint in these application fields relative to the current petrochemical value chain. This analysis and discussion differs significantly from a viewpoint on CO2 utilization as a measure for global CO2 mitigation. Whereas the latter focuses on reducing the end-of-pipe problem “CO2 emissions” from todays’ industries, the approach taken here tries to identify opportunities by exploiting a novel feedstock that avoids the utilization of fossil resource in transition toward more sustainable future production. Thus, the motivation to develop CO2-based chemistry does...

Sustainable Conversion of Carbon Dioxide: An Integrated Review of Catalysis and Life Cycle Assessment

Preface 1.General Considerations 2.Basic Processes in Atomization 3.Drop Size Distributions of Sprays 4.Atomizers 5.Flow in Atomizers 6.Atomizer Performance 7.External Spray Charcteristics 8.Drop Evaporation 9.Drop Sizing Methods Index

Atomization and Sprays

The impact that anthropogenic CO2 is having on the environment has been thoroughly documented over the last 20 years. Many different technologies have been proposed to reduce its impact on global warming such as geological sequestration. However, an interesting and attractive alternative would be the recycling of the gas into energy-rich molecules. Iron rather than cobalt catalysts, based on the Fischer–Tropsch technology, have shown the greatest promise in converting CO2 to value-added hydrocarbons. The addition of co-catalysts is, however, essential to fine tune the product distribution to the more desired alkene products. The role that both the promoter and support play on the catalyst's activity is reviewed.

Heterogeneous catalytic CO2 conversion to value-added hydrocarbons

The hydrogenation of CO2 using a traditional Fischer−Tropsch Co−Pt/Al2O3 catalyst for the production of valuable hydrocarbon materials is investigated. The ability to direct product distribution was measured as a function of different feed gas ratios of H2 and CO2 (3:1, 2:1, and 1:1) as well as operating pressures (ranging from 450 to 150 psig). As the feed gas ratio was changed from 3:1 to 2:1 and 1:1, the production distribution shifted from methane toward higher chain hydrocarbons. This change in feed gas ratio is believed to lower the methanation ability of Co in favor of chain growth, with possibly two different active sites for methane and C2−C4 products. Furthermore, with decreasing pressure, the methane conversion drops slightly in favor of C2−C4 paraffins. Even though under certain reaction conditions product distribution can be shifted slightly away from the formation of methane, the catalyst studied behaves like a methanation catalyst in the hydrogenation of CO2.

Influence of Gas Feed Composition and Pressure on the Catalytic Conversion of CO2 to Hydrocarbons Using a Traditional Cobalt-Based Fischer−Tropsch Catalyst

Hydrogenation of CO2 to hydrocarbons is investigated over iron-based catalysts supported on γ-alumina to produce unsaturated hydrocarbons as feedstock chemicals for jet-fuel synthesis. Over 40% conversion levels can be achieved by doping this catalyst with Mn and K, along with an olefin/paraffin ratio of over 4. The doping levels played a crucial role in the product distribution as well as CO2 conversion yields, with over doping leading to suppression of the desirable hydrocarbon products. The characterization of the catalyst showed the presence of KAlH4 as part of the catalyst's active phase, acting as a reversible H2 reservoir and as a center for H2 activation. Characterization of the catalysts by XRD, XPS, and SEM sheds light on the role each dopant had on the overall catalyst's activity and product distribution.

Frederick W. Williams

Papers

Heterogeneous catalytic CO2 conversion to value-added hydrocarbons

Influence of Gas Feed Composition and Pressure on the Catalytic Conversion of CO2 to Hydrocarbons Using a Traditional Cobalt-Based Fischer−Tropsch Catalyst

K and Mn doped iron-based CO2 hydrogenation catalysts: Detection of KAlH4 as part of the catalyst's active phase

Chemiluminescence spectra from cool and blue flames: Electronically excited formaldehyde

C2-C5+ olefin production from CO2 hydrogenation using ceria modified Fe/Mn/K catalysts