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

Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40th anniversary since ceria was first employed by Ford Motor Company as an oxygen storage component in car converters, to become in the years since its inception an irreplaceable component in three-way catalysts (TWCs). Apart from this well-established use, ceria is looming as a catalyst component for a wide range of catalytic applications. For some of these, such as fuel cells, CeO2-based materials have almost reached the market stage, while for some other catalytic reactions, such as reforming processes, photocatalysis, water-gas shift reaction, thermochemical water splitting, and organic reactions, ceria is emerging as a unique material, holding great promise for future market breakthroughs. While much knowledge about the fundamental characteristics of CeO2-based materials has already been acquired, new characterization techniques and powerful theoretical methods are dee...

Fundamentals and Catalytic Applications of CeO2-Based Materials

Dry (CO2) reforming of methane (DRM) is a well-studied reaction that is of both scientific and industrial importance. This reaction produces syngas that can be used to produce a wide range of products, such as higher alkanes and oxygenates by means of Fischer–Tropsch synthesis. DRM is inevitably accompanied by deactivation due to carbon deposition. DRM is also a highly endothermic reaction and requires operating temperatures of 800–1000 °C to attain high equilibrium conversion of CH4 and CO2 to H2 and CO and to minimize the thermodynamic driving force for carbon deposition. The most widely used catalysts for DRM are based on Ni. However, many of these catalysts undergo severe deactivation due to carbon deposition. Noble metals have also been studied and are typically found to be much more resistant to carbon deposition than Ni catalysts, but are generally uneconomical. Noble metals can also be used to promote the Ni catalysts in order to increase their resistance to deactivation. In order to design catalysts that minimize deactivation, it is necessary to understand the elementary steps involved in the activation and conversion of CH4 and CO2. This review will cover DRM literature for catalysts based on Rh, Ru, Pt, and Pd metals. This includes the effect of these noble metals on the kinetics, mechanism and deactivation of these catalysts.

A review of dry (CO2) reforming of methane over noble metal catalysts

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

Multiwalled carbon nanotube-supported Pt (Pt/MWNT) nanocomposites were prepared by both the aqueous solution reduction of a Pt salt (HCHO reduction) and the reduction of a Pt ion salt in ethylene glycol solution. For comparison, a Pt/XC-72 nanocomposite was also prepared by the EG method. The Pt/MWNT catalyst prepared by the EG method has a high and homogeneous dispersion of spherical Pt metal particles with a narrow particle-size distribution. TEM images show that the Pt particle size is in the range of 2-5 nm with a peak at 2.6 nm, which is consistent with 2.5 nm obtained from the XRD broadening calculation. Surface chemical modifications of MWNTs and water content in EG solvent are found to be the key factors in depositing Pt particles on MWNTs. In the case of the direct methanol fuel cell (DMFC) test, the Pt/MWNT catalyst prepared by EG reduction is slightly superior to the catalyst prepared by aqueous reduction and displays significantly higher performance than the Pt/XC-72 catalyst. These differences in catalytic performance between the MWNT-supported or the carbon black XC-72-supported catalysts are attributed to a greater dispersion of the supported Pt particles when the EG method is used, in contrast to aqueous HCHO reduction and to possible unique structural and higher electrical properties when contrasting MWNTs to carbon black XC-72 as a support.

Preparation and Characterization of Multiwalled Carbon Nanotube-Supported Platinum for Cathode Catalysts of Direct Methanol Fuel Cells

The effects of different activated carbon supports and support modifications on the properties of Pt/AC catalysts

http://www.fen.bilkent.edu.tr/~ozensoy/publications/Ozensoy%20et%20al%20%20Methane%20Reforming%20IntJHydrogenEnergy%202009.pdf

The effect of impregnation strategy on methane dry reforming activity of Ce promoted Pt/ZrO2

CO2 reforming of methane over Pt–Ni/Al2O3 catalysts: Effects of catalyst composition, and water and oxygen addition to the feed

The overall purpose of this study is to propose an effective Co-based non-PGM bimetallic carbon dioxide reforming of methane (CDRM) catalyst, and to find the optimal reaction conditions to be used in production of synthesis gas. In catalyst formulation, ZrO2, which has ability to produce surface oxygen, is used as a support. Ce is used as a promoter in order to increase oxygen storage capacity and to regulate surface oxygen transfer. Freshly reduced and spent catalysts were analyzed by SEM–EDX, HRTEM–EDX, TPO, Raman Spectroscopy and XPS. The reaction conditions were optimised through the use of an experimentally designed procedure using reaction temperature, CH4/CO2 feed ratio and space velocity as the parameters. XPS analysis of Co 2p indicated that additional oxidation of Co was limited during CDRM which may only lead to a small decrease in activity. EM measurements showed well dispersion of Co and Ce on the surface. No significant metal sintering was observed. Local changes in Co/Ce ratio were found to have pronounced effect on carbon formation. It is well known that methane dehydrogenation produces surface carbon as the side product covering the active site. The comparative analysis of extent of carbon coverage on Co and Ce sites of the freshly reduced and spent samples through metal mapping by SEM–EDX indirectly confirmed methane dehydrogenation is the primary function of Co sites, and there is no methane activation on Ce sites. A comparative evaluation of XPS Ce 3d obtained from freshly reduced and spent samples on the other hand showed the surface oxygen storage/transfer function of Ce through redox cycle. In the performance tests, high activity with stable performance was observed for 1/1CH4/CO2 feed ratio for CDRM over Co–Ce/ZrO2 catalyst.

A study on characterization and methane dry reforming performance of Co–Ce/ZrO2 catalyst

A commercial activated carbon (AC) was used as a support either after washing with HCl or after further oxidation with air or HNO 3  The supports were characterized by N 2 adsorption, TPD and SEM The results indicated the drastic change in physical and surface chemical properties of activated carbons due to the oxidation treatments Three sets of catalysts were prepared on these supports In each set, monometallic Pt/AC and bimetallic Pt–Sn/AC catalysts were prepared Bimetallic catalysts were prepared either by coimpregnation or by sequential impregnation in which the Sn precursor was introduced first In all catalysts, the Pt loading was kept fixed as 1 wt% Two levels of Sn loading, 025 and 050 wt%, were applied in bimetallic samples The catalysts were characterized by H 2 adsorption, TPR, SEM-EDX, XRD, XPS and tested in a structure insensitive reaction (benzene hydrogenation) The results indicated the pronounced changes in catalytic properties depending on the abundance of surface oxide groups of the supports and Pt–Sn interaction Coimpregnation favored Pt–Sn interaction and alloy formation The type of alloy formed was affected by the surface chemistry of the activated carbon; oxidized samples favored the formation of Pt 3 Sn XPS results indicated the migration of Pt from surface to interior sites which is driven by decomposition of oxygen bearing anchoring sites during the reduction The migration was stabilized up to a point by the introduction of Sn as the second metallic phase and, as a consequence, by the Pt–Sn interaction The interaction between metallic phases and alloy formation led to striking decreases in benzene hydrogenation activity, which indicates the lower amount of active Pt sites available Very high H 2 adsorption capacities of bimetallic samples compared to their benzene hydrogenation activities point out to the H 2 adsorption capacities of the Pt–Sn alloys formed

A. Erhan Aksoylu

Papers

The effects of different activated carbon supports and support modifications on the properties of Pt/AC catalysts

The effect of impregnation strategy on methane dry reforming activity of Ce promoted Pt/ZrO2

CO2 reforming of methane over Pt–Ni/Al2O3 catalysts: Effects of catalyst composition, and water and oxygen addition to the feed

A study on characterization and methane dry reforming performance of Co–Ce/ZrO2 catalyst

Bimetallic Pt–Sn catalysts supported on activated carbon: I. The effects of support modification and impregnation strategy