Nanomaterials as catalysts for CO2 transformation into value-added products: A review

Carbon dioxide (CO₂₎ is the most important greenhouse gas (GHG), accounting for 76% of all GHG emissions. The atmospheric CO₂ concentration has increased from 280 ppm in the pre-industrial era to about 418 ppm, and is projected to reach 570 ppm by the end of the 21^st century. In addition to reducing CO₂ emissions from anthropogenic activities, strategies to adequately address climate change must include CO₂ capture. To promote circular economy, captured CO₂ should be converted to value-added materials such as fuels and other chemical feedstock. Due to their tunable chemistry (which allows them to be selective) and high surface area (which allows them to be efficient), engineered nanomaterials are promising for CO₂ capturing and/or transformation. This work critically reviewed the application of nanomaterials for the transformation of CO₂ into various fuels, like formic acid, carbon monoxide, methanol, and ethanol. We discussed the literature on the use of metal-based nanomaterials, inorganic/organic nanocomposites, as well as other routes suitable for CO₂ conversion such as the electrochemical, non-thermal plasma, and hydrogenation routes. The characteristics, steps, mechanisms, and challenges associated with the different transformation technologies were also discussed. Finally, we presented a section on the outlook of the field, which includes recommendations for how to continue to advance the use of nanotechnology for conversion of CO₂ to fuels.

Porous LaFeO3 perovskite catalysts synthesized by different methods and their high activities for CO oxidation

In this study, spherical α-Fe₂O₃ prepared by the hydrothermal method was used as a template for the first time; LaFeO₃ perovskite catalysts were successfully synthesized by the molten salt method (M-LF-T), sol-gel method (S-LF-T), and co-precipitation method (C-LF-T), respectively. To determine the optimal synthesis method, X-ray diffraction patterns were obtained and showed that single phase LaFeO₃ with good crystallinity was prepared by the molten salt method after calcination at 600 °C for 4 h. SEM and TEM images showed that the M-LF-600 catalyst preserved the spherical structure of α-Fe₂O₃ template. Compared with the catalysts synthesized by the sol-gel method and co-precipitation method, the M-LF-600 catalyst had the highest BET surface area of 16.73 m² g^-1. X-ray photoelectron spectroscopy analysis showed that the M-LF-600 catalyst had the highest surface Fe³⁺/Fe²⁺ molar ratio and the best surface oxygen adsorption capacity. The CO oxidation of the LaFeO₃ catalyst demonstrated that the M-LF-600 catalyst had the best catalytic performance.

Emerging natural and tailored perovskite-type mixed oxides–based catalysts for CO2 conversions

The rapid economic and societal development have led to unprecedented energy demand and consumption resulting in the harmful emission of pollutants. Hence, the conversion of greenhouse gases into valuable chemicals and fuels has become an urgent challenge for the scientific community. In recent decades, perovskite-type mixed oxide-based catalysts have attracted significant attention as efficient CO2 conversion catalysts due to the characteristics of both reversible oxygen storage capacity and stable structure compared to traditional oxide-supported catalysts. In this review, we hand over a comprehensive overview of the research for CO2 conversion by these emerging perovskite-type mixed oxide-based catalysts. Three main CO2 conversions, namely reverse water gas shift reaction, CO2 methanation, and CO2 reforming of methane have been introduced over perovskite-type mixed oxide-based catalysts and their reaction mechanisms. Different approaches for promoting activity and resisting carbon deposition have also been discussed, involving increased oxygen vacancies, enhanced dispersion of active metal, and fine-tuning strong metal-support interactions. Finally, the current challenges are mooted, and we have proposed future research prospects in this field to inspire more sensational breakthroughs in the material and environment fields.

Oxidative coupling of bio-alcohols mixture over hierarchically porous perovskite catalysts for sustainable acrolein production

The acrolein production from bio-alcohols methanol and ethanol mixtures using AMnO3 (since A = Ba and/or Sr) perovskite catalysts was studied. All the prepared samples were characterized by XRD, XPS, N2 sorption, FTIR, Raman spectroscopy, TEM, SEM, TGA, and NH3-CO2-TPD. The catalytic oxidation reaction to produce acrolein has occurred via two steps, the alcohols are firstly oxidized to corresponding aldehydes, and then the aldol is coupled with the produced aldehydes. The prepared perovskite samples were modified by doping A (Sr) position with (Ba) to improve the aldol condensation. The most catalytic performance was achieved using the BaSrMnO3 sample in which the acrolein selectivity reached 62% (T = 300 °C, MetOH/EtOH = 1, LHSV = 10 h-1). The increase in acrolein production may be related to the high tendency of BaSrMnO3 toward C-C coupling formation. The C-C tendency attributes to that modification have occurred in acid/base sites because of metal substitution.

State of the art and perspectives in heterogeneous catalysis of CO2 hydrogenation to methanol

The ever-increasing amount of anthropogenic carbon dioxide (CO₂) emissions has resulted in great environmental impacts, the heterogeneous catalysis of CO₂ hydrogenation to methanol is of great significance.

Integrated Experimental-Theoretical Approach To Determine Reliable Molecular Reaction Mechanisms on Transition-Metal Oxide Surfaces

By combining experimental and theoretical approaches, we investigate the quantitative relationship between molecular desorption temperature and binding energy on d and f metal oxide surfaces. We demonstrate how temperature-programmed desorption can be used to quantitatively correlate the theoretical surface chemistry of metal oxides (via on-site Hubbard U correction) to gas surface interactions for catalytic reactions. For this purpose, both CO and NO oxidation mechanisms are studied in a step-by-step reaction process for perovskite and mullite-type oxides, respectively. Additionally, we show solutions for over-binding issues found in CO_x, NO_x, SO_x, and other covalently bonded molecules that must be considered during surface reaction modeling. This work shows the high reliability of using TPD and density functional theory in conjunction to create accurate surface chemistry information for a variety of correlated metal oxide materials.

Ni-Sn-Supported ZrO2 Catalysts Modified by Indium for Selective CO2 Hydrogenation to Methanol

Ni and NiSn supported on zirconia (ZrO₂) and on indium (In)-incorporated zirconia (InZrO₂) catalysts were prepared by a wet chemical reduction route and tested for hydrogenation of CO₂ to methanol in a fixed-bed isothermal flow reactor at 250 °C. The mono-metallic Ni (5%Ni/ZrO₂) catalysts showed a very high selectivity for methane (99%) during CO₂ hydrogenation. Introduction of Sn to this material with the following formulation 5Ni5Sn/ZrO₂ (5% Ni-5% Sn/ZrO₂) showed the rate of methanol formation to be 0.0417 μmol/(g_cat·s) with 54% selectivity. Furthermore, the combination NiSn supported on InZrO₂ (5Ni5Sn/10InZrO₂) exhibited a rate of methanol formation 10 times higher than that on 5Ni/ZrO₂ (0.1043 μmol/(g_cat·s)) with 99% selectivity for methanol. All of these catalysts were characterized by X-ray diffraction, high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy, CO₂-temperature-programmed desorption, and density functional theory (DFT) studies. Addition of Sn to Ni catalysts resulted in the formation of a NiSn alloy. The NiSn alloy particle size was kept in the range of 10-15 nm, which was evidenced by HRTEM study. DFT analysis was carried out to identify the surface composition as well as the structural location of each element on the surface in three compositions investigated, namely, Ni₂₈Sn₂₇, Ni₁₈Sn₃₇, and Ni₃₇Sn₁₈ bimetallic nanoclusters, and results were in agreement with the STEM and electron energy-loss spectroscopy results. Also, the introduction of "Sn" and "In" helped improve the reducibility of Ni oxide and the basic strength of catalysts. Considerable details of the catalytic and structural properties of the Ni, NiSn, and NiSnIn catalyst systems were elucidated. These observations were decisive for achieving a highly efficient formation rate of methanol via CO₂ by the H₂ reduction process with high methanol selectivity.

Facile synthesis of porous spherical La0.8Sr0.2Mn1−xCuxO3(0 ≤x≤ 0.4) and nanocubic La0.8Sr0.2MnO3with high catalytic activity for CO

A molten salt method has been used to prepare porous La_0.8Sr_0.2Mn_1−xCu_xO₃(0 ≤x≤ 0.4) (LSMC-X) microspheres and La_0.8Sr_0.2MnO₃(LSM) nanocubes using spherical and cubic MnCO₃as templates, respectively.

Copper doped BaMnO3 perovskite catalysts for NO oxidation and NO2-assisted diesel soot removal

BaMn_0.7Cu_0.3O₃ is the most active catalyst for NO₂ generation and soot oxidation. This behavior is a result of the enhancement of the redox properties of the catalyst due to the replacement of Mn(iii)/Mn(iv) by Cu(ii) in the perovskite structure.

Effect of A/B-site substitution on oxygen production performance of strontium cobalt based perovskites for CO2 capture application

Oxy-fuel combustion is one of the proposed technologies which have the potential to achieve zero CO₂ emission.