CO2 as an Oxidant for High-Temperature Reactions

Abstract

This paper presents a review on the developments in catalyst technology for the reactions utilizing CO 2 for high-temperature applications. These include dehydrogenation of alkanes to olefins, the dehydrogenation of ethylbenzene to styrene, and finally CO 2 reforming of hydrocarbon feedstock (i.e., methane) and alcohols. Aspects on the various reaction pathways are also highlighted. The literature on the role of promoters and catalyst development is critically evaluated. Most of the reactions discussed in this review are exploited in industries and related to on-going processes, thus providing extensive data from literature. However, some reactions, such as CO 2 reforming of ethanol and glycerol, which have not reached industrial scale, are also reviewed owing to their great potential in terms of sustainability, which is essential as energy for the future. This review further illustrates the building-up of knowledge that shows the role of support and catalysts for each reaction and the underlying linkage between certain catalysts, which can be adapted for the multiple CO 2 -related reactions.

Silica-Related Catalysts for CO2 Transformation into Methanol and Dimethyl Ether

“…Deglaciation, global warming, increasingly frequent and devastating meteorological phenomena (hurricanes, typhoons, torrential rains, earthquakes, etc.) are directly related to the climate change that the planet is suffering, mainly as a consequence of emissions of greenhouse gases to the atmosphere [1]. Among these gases, it is estimated that CO 2 causes around 70% of global warming [2], thus being the main greenhouse gas.…”

“…The scientific community has proposed a wide range of possibilities to use CO 2 to produce high-value-added products through catalytic processes, such as dry reforming of methane [12], copolymerization reactions [13], oxidative dehydrogenation (ODH) of light alkanes [14], methanation [15], oxidative coupling of methane [16] or hydrogenation of carbon dioxide, among others, so that a CO 2 closed cycle can be established, where "spent carbon" such as CO 2 is converted into "working carbon" that is present in valuable chemicals or fuels. However, the CO 2 molecule has a high oxidation state and is also very thermodynamically stable (∆G f = −396 kJ•mol −1 ), it must be combined with high-energy reagents, together with effective catalysts and at the conditions of thermodynamically favorable reaction [1] to obtain high value-added or combustible products. Therefore, the development of processes and/or products that are less harmful to the environment and mainly focused on reducing global warming is one of the main challenges facing the scientific community.…”

Chemical looping syngas from CO2 and H2O over manganese oxide minerals

“…Bi‐reforming of methane, a combination of steam and reforming, yielding and CO in a 2:1 ratio (i.e. ideal for the production of methanol), is another emerging technology. However, both dry and bi‐reforming rely on the use of methane.…”

“… is an emerging feedstock for: i) fuels (methane, methanol); ii) commodity chemicals via hydrogenation (e.g. formaldehyde, formic acid); iii) olefins from dehydrogenation of alkanes; iv) styrene via dehydrogenation of ethylbenzene; v) dry reforming of methane, alcohols, and glycerol; and vi) direct splitting into CO. inhibits coking of catalysts, increases olefins yield (alkane dehydrogenation), and improves styrene selectivity …”

“…formaldehyde, formic acid); iii) olefins from dehydrogenation of alkanes; [13] iv) styrene via dehydrogenation of ethylbenzene; v) dry reforming of methane, alcohols, and glycerol; and vi) direct splitting into CO. CO 2 inhibits coking of catalysts, increases olefins yield (alkane dehydrogenation), and improves styrene selectivity. [13] Three major axis to split CO 2 are under development: i) thermochemical non-catalytic and catalytic gas-solid CO 2 reduction; ii) light-driven photocatalytic reduction; and iii) electrochemical reduction for fuel cells. [27] Similarly to photocatalytic water splitting, CO 2 photocatalysts are unable to split CO 2 under visible light.…”