Crystallization behavior of zirconium oxide gels

Efficient catalyst design has garnered significant interest in recent decades due to its potential to address both the challenges of the greenhouse effect and energy shortages by facilitating the conversion of CO2 into valuable chemicals through catalytic reactions. To investigate maximizing the synergistic effects of supported PdAu catalysts, we conducted first-principles calculations on the activation and decomposition of CO2 and H2 on the PdAu/In2O3(110) system. The results demonstrate that the incorporation of a secondary metal (Au) into the supported Pd catalyst, in conjunction with precise control over Au concentration, exerts influence on both reactant binding energy and activation. The adsorption and activation of CO2 at the interface sites of Au4/In2O3(110) and PdAu3/In2O3(110) are not observed. The transition state for the dissociation of CO2 into *CO and *O is determined based on adsorbed CO2, providing insights into the properties of activated CO2. The Bronsted–Evans–Polanyi relation, which correlates activation barriers (Ea) with reaction energies (Er), was established for the CO2 dissociation mechanism on PdAu/In2O3(110) catalysts using equation E = 0.4Ea + 0.63. It was carried out to investigate the H2-dissociated adsorption processes and mobility energy on various PdAu/In2O3(110) catalysts. Finally, a highly efficient Pd2Au2/In2O3 catalyst for the hydrogenation of CO2 into methanol has been proposed. This research provides valuable insights into the hydrogenation of CO2 to methanol using bimetal-oxide catalysts and contributes to the optimization of the design of PdAu/In2O3 catalysts for CO2 reactions.

Many oxide catalysts exhibit high selectivity but low conversion in CO2 hydrogenation due to strong CO2 adsorption, which often impedes H2 dissociation and subsequent hydrogenation. Herein, we report that a ZnCr2O4@ZnOx catalyst featuring monodispersed ZnOx overlayer confined on ZnCr2O4 facilitates CO2 activation without compromising H2 activation. This catalyst demonstrates a dual-site mechanism in which ZnCr2O4 surface and/or ZnOx/ZnCr2O4 interface provide sites for CO2 activation and monodispersed ZnOx promote homolytic H2 dissociation and formation of stable metal─H species, enabling formate formation through hydrogen spillover to CO2 adsorption sites for hydrogenation at 303K. In contrast, H2 activation on ZnO or ZnCr2O4 suffers from the poisoning effect of strong CO2 adsorption. Consequently, the ZnCr2O4@ZnOx catalyst shows 2-8 folds enhancement in CO2 hydrogenation between 623-773K than ZnO and maintains 33% conversion and 100% CO selectivity at 723K over 150h. The established structure-performance relationship illustrates the critical role of dual-site catalysis and hydrogen spillover in hydrogenation reaction.

Zn-CdZrOx solid solution catalysts for hydrogenation of CO2 to methanol

A review on the catalytic conversion of CO2 using H2 for synthesis of CO, methanol, and hydrocarbons

The influence of the compositions and structures of Cu-ZrO2 catalysts on the catalytic performance of CO2 hydrogenation to CH3OH

The catalytic hydrogenation of carbon dioxide (CO2) to methanol under mild conditions presents a sustainable route for carbon recycling and chemical energy storage. However, the inert nature of CO2 and high activation energy barrier for methanol formation remain major challenges. In this study, we developed a series of Nb-promoted Pt/MoOx/TiO2 catalysts for efficient CO2 hydrogenation at temperatures below 200°C. Among these, Pt(5)/Mo(10)-Nb(1)/TiO2 exhibited superior performance, achieving a high methanol productivity of 3.8mmol gcat -1 h-1 at 150°C, outperforming the commercial Cu-ZnO/Al2O3 catalyst under comparable conditions. The catalyst showed stable performance during a 400h long-term reaction. Detailed in situ and operando spectroscopic studies revealed that Pt sites were primarily responsible for H2 activation, while partially reduced MoOx species facilitated the formation of oxygenated intermediates. The incorporation of highly dispersed Nb species promoted methanol desorption and inhibited its decomposition, thereby contributing to the overall catalytic efficiency. This study outlines a rational design approach for constructing robust low-temperature catalysts and provides mechanistic insights into the synergistic roles of the metal and oxide components in CO2-to-methanol conversion.

Pd/ZnO catalysts with ca. 2 wt.% Pd loading employing ZnO nanocrystals with various morphologies as supports, including ZnO nanoplates (p−ZnO) predominantly exposing polar {002} facets, ZnO nanorods (r−ZnO) predominantly exposing nonpolar {100} and {101} facets, and commercial ZnO (c−ZnO) exposing random facets, have been prepared as catalysts for the catalytic reaction of CO2 hydrogenation into formic acid (FA) without the addition of base under mild conditions. A remarkable morphology‐dependence of zinc oxide in the Pd/ZnO catalysts was observed. Catalytic activities of various Pd/ZnO catalysts in CO2 hydrogenation into FA follow an order of Pd/r−ZnO>Pd/p−ZnO>Pd/c−ZnO, and all the catalysts are stable. Kinetic study, CO2‐TPD analysis, and in situ DRIFTS spectra provide evidence that all the Pd/ZnO catalysts follow a similar catalytic mechanism that CO2 activation is the rate‐determining step. Consequently, r−ZnO, possessing a higher density of weak basic sites than p−ZnO and c−ZnO, can act as a superb support to prepare Pd/r−ZnO catalyst, which is more active than Pd/p−ZnO and Pd/c−ZnO catalysts for the production of FA. These findings nicely demonstrate the crystal‐plane engineering of the metal oxide support in tuning the catalytic performance of Pd‐based catalysts for CO2 hydrogenation into FA.

Effect of unimodal and bimodal MCM-41 mesoporous silica supports on activity of Fe–Cu catalysts for CO2 hydrogenation

Study on the performance of F-T component modified KCuZrO2 catalyst for CO hydrogenation to isobutanol

Effect of Ba and K addition and controlled spatial deposition of Rh in Rh/Al2O3 catalysts for CO2 hydrogenation

The hydrogenation of CO2 to high-value-added liquid fuels is crucial for greenhouse gas emission reduction and optimal utilization of carbon resources. Developing supported heterogeneous catalysts is a key strategy in this context, as they offer well-defined active sites for in-depth mechanistic studies and improved catalyst design. Here, we conducted extensive first-principles calculations to systematically explore the reaction mechanisms for CO2 hydrogenation on a heterogeneous bimetal NiAl-deposited metal-organic framework (MOF) NU-1000 and its catalytic performance as atomically dispersed catalysts for CO2 hydrogenation to formic acid (HCOOH), formaldehyde (H2CO), and methanol (CH3OH). The present results reveal that the presence of the NiAl-oxo cluster deposited on NU-1000 efficiently activates H2, and the facile heterolysis of H2 on Ni and adjacent O sites serves as a precursor to the hydrogenation of CO2 into various C1 products HCOOH, H2CO, and CH3OH. Generally, H2 activation is the rate-determining step in the entire CO2 hydrogenation process, the corresponding relatively low free energy barriers range from 14.5 to 15.9 kcal/mol, and the desorption of products on NiAl-deposited NU-1000 is relatively facile. Although the Al atom does not directly participate in the reaction, its presence provides exposed oxygen sites that facilitate the heterolytic cleavage of H2 and the hydrogenation of C1 intermediates, which plays an important role in enhancing the catalytic activity of the Ni site. The present study demonstrates that the catalytic performance of NU-1000 can be finely tuned by depositing heterometal-oxo clusters, and the porous MOF should be an attractive platform for the construction of atomically dispersed catalysts.

A Mo-based catalyst (catalyst I) was prepared under microwave irradiation, and characterized with X-ray diffractometer, X-ray fluorescence spectrometry, nitrogen adsorption, Fourier transform infrared spectrometer, and scanning electron microscope. The activity of catalyst I for CO hydrogenation was studied in comparison with another Mo-based catalyst (catalyst II) prepared by conventional heating methods. The results show that CO conversion reached a maximum with temperatures up to 240°C over either of the catalysts. However, CO conversion and selectivities of methanol and dimethyl ether over catalyst I were higher than those over catalyst II, indicating that microwave irradiation favors the preparation of Mo-based catalyst for CO hydrogenation catalyst.

Nitrogen‐doped, bamboo‐like carbon nanotubes (BCNTs) were synthesized from butylamine by catalytic chemical vapor deposition (CCVD method). The nanotubes were oxidized by H2SO4/HNO3 treatment and used to prepare calcium alginate gelled BCNT spheres. These beads were first carbonized and then Pd, Rh and Ni nanoparticles were anchored on the surface of the spheres. These systems were then applied as catalysts in CO2 hydrogenation. The BCNT support was examined by Raman spectroscopy, dynamic light scattering (DLS) and X‐ray photoelectron spectroscopy (XPS). The prepared catalysts were characterized by HRTEM and SEM. The oxidation pretreatment of BCNTs was successful, with the electrokinetic potential of the water‐based dispersion of BCNTs measuring −59.9 mV, meaning the nanotube dispersion is stable. Pyridinic and graphitic types of incorporated nitrogen centers were identified in the structure of the nanotubes, according to the XPS measurements. The Pd‐containing BCNT sphere catalyst was the most efficient in the catalytic studies. The highest conversion was reached on the Pd catalyst at 723 K, as well as at 873 K. The difference in the formation rate of CO was much less at 873 K between the Pd and Rh compared to the 723 K values. Accordingly, the application of Pd‐containing BCNT/carbon‐supported catalyst favored the generation of CO. However, the Ni‐BCNT/carbon catalyst leads to the formation of CH4 as the major product.

Currently, the Cu-based catalyst has become a promising candidate for ethanol and higher alcohols synthesis (HAs) from synthesis gas (H2 + CO), but all these catalysts contain F–T elements (e.g., Co and Fe) and alkalis because carbon chain growth reaction occurs on these metal components. Herein, two series of ternary CuZnAlOOH catalysts with various Cu and Al proportions were synthesized using a complete liquid-phase method and studied in the conversion of syngas in a slurry bed reactor. Significantly higher selectivity of ethanol (40 wt %) and HA (65 wt %) with approximately 20% CO conversion was achieved when the n(Cu)/n(Al) = 2/0.8, which was ascribed the highest copper surface area (SCu) and the surface Cu content. It was found that the Cu component had a significant effect on CO conversion, while the Al component had more influence on the selectivity of HA. Besides, the coke deposition was discovered to be the main reason for catalyst deactivation. The generation of hydrocarbons and alcohols followed A–S–F distributions, which was consistent with a representative mechanism of HA generation by CO insertion into the CHx intermediate. A synergetic mechanism between Cu0–Cu+ and AlOOH active sites was proposed based on the characterization analysis and activity results, in which Cu0–Cu+ synergy acted as sites for H2 dissociative adsorption and associative adsorption of CO, while the AlOOH facilitated the dissociation of the C–O bond. Bifunctionality of the Cu and AlOOH active sites and their cooperation created their synergy in CO hydrogenation to ethanol and HA. This work provided us a new concept to understand and develop carbon chain growth mechanism, and it also could provide reference for other related carbon chain growth reactions.

A surface science investigation of the role of potassium promoters in nickel catalysts for CO hydrogenation