The chemical transformation of CO2 not only mitigates the anthropogenic CO2 emission into the Earth’s atmosphere but also produces carbon compounds that can be used as precursors for the production of chemicals and fuels. The activation and conversion of CO2 can be achieved on multifunctional catalytic sites available at the metal/oxide interface by taking advantage of the synergy between the metal nanoparticles and oxide support. Herein, we look at the recent progress in mechanistic studies of CO2 hydrogenation to C1 (CO, CH3OH, and CH4) compounds on metal/oxide catalysts. On this basis, we are able to provide a better understanding of the complex reaction network, grasp the capability of manipulating structure and combination of metal and oxide at the interface in tuning selectivity, and identify the key descriptors to control the activity and, in particular, the selectivity of catalysts. Finally, we also discuss challenges and future research opportunities for tuning the selective conversion of CO2 on ...

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Tuning Selectivity of CO2 Hydrogenation Reactions at the Metal/Oxide Interface

The surface and interfaces of heterogeneous catalysts are essential to their performance as they are often considered to be active sites for catalytic reactions. With the development of nanoscience, the ability to tune surface and interface of nanostructures has provided a versatile tool for the development and optimization of a heterogeneous catalyst. In this Review, we present the surface and interface control of nanoparticle catalysts in the context of oxygen reduction reaction (ORR), electrochemical CO2 reduction reaction (CO2 RR), and tandem catalysis in three sections. In the first section, we start with the activity of ORR on the nanoscale surface and then focus on the approaches to optimize the performance of Pt-based catalyst including using alloying, core-shell structure, and high surface area open structures. In the section of CO2 RR, where the surface composition of the catalysts plays a dominant role, we cover its reaction fundamentals and the performance of different nanosized metal catalysts. For tandem catalysis, where adjacent catalytic interfaces in a single nanostructure catalyze sequential reactions, we describe its concept and principle, catalyst synthesis methodology, and application in different reactions.

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Surface and Interface Control in Nanoparticle Catalysis.

Catalytic conversion of CO2 to chemicals and fuels is a “two birds, one stone” approach toward solving the climate change problem and energy demand–supply deficit in the modern world. Recent advances in mechanistic insights and design of suitable catalysts for direct thermocatalytic hydrogenation of CO2 to C1 products are thoroughly discussed in this Review. The role of catalyst composition and process conditions in determining the selective pathways to various products like carbon monoxide, methanol, methane, and dimethyl ether has been overviewed in light of thermodynamic and kinetic considerations. After extensive elaboration of the main motivation of the reaction pathways, catalytic roles, and reaction thermodynamics, we summarize the most important macroscopic aspects of CO2 hydrogenation technology development, which include reactor innovations, industrial status of the technology, life cycle assessment and technoeconomic analysis. Finally, a critical perspective on the future challenges and opportu...

Thermochemical CO2 Hydrogenation to Single Carbon Products: Scientific and Technological Challenges

Cu-oxide catalysts have a tendency to deactivate dramatically in reverse water gas shift (RWGS) reaction, because of the aggregation of supported copper particles at high temperatures. Herein, β-Mo2C, which is a typical type of transition-metal carbide, has been demonstrated to be capable of dispersing and stabilizing copper particles. Cu/β-Mo2C catalysts exhibit good catalytic activity and stability for the RWGS reaction. Under relatively high weight hourly space velocity (WHSV = 300 000 mL/g/h), the optimized 1 wt % Cu/β-Mo2C exhibits superior activity over traditional oxide-supported Pt- and Cu-based catalysts. The activity was well-maintained in a 40 h stability test, and the catalyst shows stable reactivity in a six-cycle start-up cool-down experiment. Detailed structure characterizations demonstrate that the strong interaction between Cu and β-Mo2C effectively promotes the dispersion of supported copper and prevents the aggregation of Cu particles, which accounts for the extraordinary activity and s...

Highly Dispersed Copper over β-Mo2C as an Efficient and Stable Catalyst for the Reverse Water Gas Shift (RWGS) Reaction

Multifunctional smart windows are successfully fabricated by assembling inkjet printed CeO2/TiO2 and WO3/poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) films as the anode and cathode, respectively. Large optical modulation (more than 70% at 633 nm), fast switching (12.7/15.8 s), high coloration efficiency (108.9 cm2 C−1), and excellent bistability are achieved by the assembled smart windows. The multifunctional smart window not only can be used as typical electrochromic window, which can change its color to dynamically control the solar radiation transmittance through windows or protect privacy during the day, but also can be used as energy-storage device simultaneously. The designed smart window releases the stored energy to light the bulbs and power other electronic devices at night while its color gradually reverts to transparent state. Moreover, the level of stored energy can be monitored via the visually detectable reversible color variation of the window. The fascinating multifunctional smart windows exhibit promising features for a wide range of applications in buildings, airplanes, automobiles, etc.

Inkjet Printed Large Area Multifunctional Smart Windows

In this study, the effect of the reducibility of the support on the mechanism of the reverse water gas shift reaction over Pt/TiO 2 and Pt/Al 2 O 3 catalysts was examined using a differential and fixed bed reactor. The kinetic study showed that the reverse water gas shift reaction using the Pt/TiO 2 and Pt/Al 2 O 3 catalysts were consistent with the redox mechanism. An elementary reaction test and XPS analysis further confirmed that the reverse water gas shift reaction proceeded through the redox mechanism via oxidation and reduction at the Pt sites and reducible support sites on the catalyst surface. In the H 2 TPR and FT-IR experiments, the Pt/TiO 2 was shown to have a new active site located at the metal–support interface. Therefore, the Pt/TiO 2 catalyst produced greater CO 2 conversion and TOFs due to the presence of the new active site, which resulted from the strong metal–support interaction and higher reducibility of the support relative to the Pt/Al 2 O 3 catalyst.

A study on the effect of support's reducibility on the reverse water-gas shift reaction over Pt catalysts

Herein, 10 wt% Ce/TiO 2 catalysts were prepared via wet impregnation at different calcination temperatures and used for selective catalytic oxidation (SCO) of NH 3 to N 2  The 10 wt% Ce/TiO 2 catalyst calcined at 400 °C showed the highest NH 3 conversion (∼96%) and N 2 (∼93%) yield (at 350 °C) As determined by BET and XRD studies, the ceria oxides existed in either highly dispersed or amorphous phases after preparation at low calcination temperatures ( 2 catalysts were investigated using TPR, TPD, XPS, and in situ FT-IR spectroscopy The activity for the SCO of NH 3 to N 2 of the 10 wt% Ce/TiO 2 catalysts prepared at different calcination temperatures depend on the oxidation states of the Ce species and behavior of oxygen within the catalyst The SCO of NH 3 to N 2 over Ce/TiO 2 calcined at 400 °C follows an internal selective catalytic reduction mechanism

Influence of calcination temperature on Ce/TiO2 catalysis of selective catalytic oxidation of NH3 to N2

The effect of the morphological characteristics of a TiO 2 support on the reverse water–gas shift reaction over Pt/TiO 2 catalysts was examined. The activity of Pt catalysts with 6 different types of TiO 2 supports varied during the reverse water–gas shift reaction. Analysis using H 2 Temperature Programmed Reduction (TPR) and Temperature Programmed Desorption (TPD) confirmed that the active sites of the Pt/TiO 2 catalyst included both the Pt sites and the TiO 2 sites, which were reducible, and the difference in the activity of the Pt/TiO 2 catalysts was dependent on the reducibility of the TiO 2 supports. X-ray diffraction (XRD) analysis showed that the TiO 2 crystallite size was a key factor that dictated the reducibility of the TiO 2 sites.

The effect of the morphological characteristics of TiO2 supports on the reverse water–gas shift reaction over Pt/TiO2 catalysts

In this study, a catalytic membrane with controlled pore size and structure was fabricated with nano sized particles and used in a steam and dry reforming reaction. The catalytic membrane was made using uniaxial-pressing and thermal treatment of the mixed powder. Nano sized yttria stabilized ZrO2 added to the nickel powder was determined to be a key factor in the preparation of the catalytic membrane. The membrane did not show the sintering effect due to the hindering of nickel agglomeration when subjected to heat treatment at high temperature. The optimum yttria stabilized ZrO2 content was below 1 wt% due to its strength and porosity. It was also unnecessary to deposit an additional reforming catalyst on the catalytic membrane, since the surface nickel site displayed excellent catalytic activity. When a mixture of methane and water/carbon dioxide was fed into the YSZ-Ni catalytic membrane reactor, the activity trended exceeded the performance of a conventional catalyst reactor, because of the difference in the flux of the gases.

Hyun Hee Lee

Papers

A study on the effect of support's reducibility on the reverse water-gas shift reaction over Pt catalysts

Influence of calcination temperature on Ce/TiO2 catalysis of selective catalytic oxidation of NH3 to N2

The effect of the morphological characteristics of TiO2 supports on the reverse water–gas shift reaction over Pt/TiO2 catalysts

Pore control using the nano structured powders on the fabrication of porous membrane and its application.