The Mechanism of Interfacial CO₂ Activation on Al Doped Cu/ZnO

Abstract

We report on a combined quantitative charge carrier and catalytic activity analysis of Cu/ZnO­(:Al) model catalysts. The promoting effect of Al3+ on the ZnO support for CO2 activation via the reverse water–gas-shift reaction has been investigated. The contact-free and operando microwave Hall Effect technique is applied to measure charge carriers in Cu/ZnO­(:Al) based model catalysts under reverse water–gas shift reaction conditions. This method allows us to monitor the electrical conductivity, charge carrier mobility, and absolute number of charge carriers. An increase in charge carrier concentration with increasing Al3+ content and its direct correlation with the catalytic activity for CO formation is found. We conclude that the increased availability of charge carriers plays a key role in CO2 activation and CO formation, which finds additional support in a concurrent decrease of the apparent activation energy and increase in the reaction order of CO2. In combination with comprehensive DFT calculations, the impact of the interfacial charge transfer, coupled to oxygen defect sites in ZnO and CO2 adsorption properties, is elucidated and highlighted. In conclusion, the results from this operando investigation combined with DFT calculations demonstrate the importance of charge transfer processes as decisive descriptors for understanding and explaining catalytic properties.

Enhanced CO2 Hydrogenation to Methanol on the Mesostructured Cu–ZnO/Al2O3–ZrO2 Catalyst

“…The chemical nature of Zn was found to play an essential role in CO 2 hydrogenation to methanol Figure C shows the XAES spectra of Zn LMM in the treated catalysts, and there were two peaks at around 498 and 495 eV, which were ascribed to Zn 2+ and Zn 0 species, respectively .…”

“…The chemical nature of Zn was found to play an essential role in CO 2 hydrogenation to methanol. 6 Figure 10C shows the XAES spectra of Zn LMM in the treated catalysts, and there were two peaks at around 498 and 495 eV, which were ascribed to Zn 2+ and Zn 0 species, respectively. 38 It could be found that the surface concentration of Zn species was decreased with the addition of ZrO 2 in these catalysts from the intensity of Zn XAES signals, which should be caused by the strong metal−support interaction.…”

“…The CO 2 emission into the atmosphere is continuously and rapidly increasing, which causes some serious environmental and ecology problems, for instance, global warming and climate change. − Meanwhile, the demand for raw materials and energy is also significantly increasing, which has resulted in tremendous energy and environmental pressures . Therefore, many strategies have been proposed to develop the renewable energy sources and substitutable fuels from non-fossil sources to solve the environmental issues and imminent energy shortage. − Among them, CO 2 hydrogenation to methanol is considered to be one of the most prospective ways to abate the CO 2 emission and alleviate the energy shortage. , Many achievements have been acquired in hydrogenation of CO 2 to methanol. For example, CO 2 could be catalyzed to methanol by ZnO x or In 2 O 3 supported on ZrO 2 at high temperature (593–673 K). , The supported Cu catalyst decreased the reaction temperature, which showed excellent catalytic performance in a range of 513–543 K. , Meanwhile, the catalyst Cu/ZnO/Al 2 O 3 prepared via the co-precipitation method was widely used in the hydrogenation of CO 2 to methanol, and Cu steps decorated with Zn atoms in Cu/ZnO/Al 2 O 3 were considered to be the active sites and Al 2 O 3 was used as a structural promoter .…”

Highly Efficient CO2 Hydrogenation to Methanol over the Mesostructured Cu/AlZnO Catalyst

“…In addition, the chemical nature of Zn was related to the production of methanol in CO 2 hydrogenation. [28] Figure 8B showed the XAES spectra of Zn LMM in the treated catalysts, and there were two peaks around 498 and 495 eV, which were ascribed to Zn 2 + and Zn 0 species, respectively. [29] The presence of Zn 0 species on the treated catalysts should be attributed to the reduction of Zn 2 + species interacted with metallic Cu by the dissociated hydrogen on dispersed Cu, and the binding energy of Zn 0 species was weakened with the increase of ZnO, which probably was ascribed to the electron injection from the ZnO x conduction band to Cu.…”

Reverse water-gas shift reaction over Pt/MoOx/TiO2: reverse Mars–van Krevelen mechanism via redox of supported MoOx

“…[7][8][9][10][11] The catalytic hydrogenation of CO2 produces several important bulk chemicals including formic acid, methanol, and hydrocarbons. 12,13,[22][23][24][14][15][16][17][18][19][20][21] Although this one-step CO2 conversion to value-added chemicals is attractive, there is difficulty associated with the fact that CO2 is kinetically unreactive and thermodynamically stable. 25,26 The catalytic hydrogenation of CO2 to CO, also called the reverse water-gas shift (RWGS: CO2 + H2 → CO +H2O) reaction, serves as a highly flexible strategy for utilization of CO2 because CO is an important intermediate in various well-established catalytic processes to manufacture value-added chemicals.…”