Catalytic Hydrogenation Of CO2 Research Articles

Template free synthesis of CuO nanocomposite for catalytic hydrogenation of CO2

Increasing CO2 emissions from industry has disastrous consequences for the environment. Effective utilization of CO2 as a carbon source can address the environmental challenges, and we can address the energy crisis caused by fossil fuel consumption. Electrochemical conversion of CO2 is a promising method recently gaining widespread popularity. Its high productivity, however, remains a major challenge. This work involved a facile novel preparation of a suitable CuO nanocomposite to reduce CO2 into useful fuels effectively. Hydrothermal synthesis was used to synthesize the nanocomposite. The synthesized NC's structure, morphology, and elemental analysis were evaluated using XRD, Raman spectroscopy, SEM, and TEM. ICP-OES analysis was performed to quantify Cu concentration in the CuO composite, confirming 98.6% of Cu of the prepared matrix. The cyclic voltammetry method has been used to study the electrochemical activity of NC for CO2 reduction. Additionally, the NMR & GC-MS analyses were performed to identify the product. Regarding CO2 reduction, the NC performed greatly better than the ordinary CuO. In addition, the NC exhibits high structural stability and durability, demonstrating its potential to reduce CO2 into fuels.

Catalytic CO2 hydrogenation to produce methane over NiO/TiO2 composite: Effect of TiO2 structure

In this study, TiO2 was morphologically engineered into three distinct structures, namely three-dimensional microparticles (MPs), zero-dimensional nanoparticles (NPs) and one-dimensional nanowires (NWs) to examine the effect of structure on CO2 methanation. Firstly, thermodynamic analysis was conducted, whereby it was observed that CH4 production is favoured at low temperature. Higher temperature will cause the CH4 selectivity to drop, in turn increasing the formation of other side products such as CO, C2H6 and solid coke. Then, Ni loaded on three different TiO2 supports, namely 3D TiO2 microparticles (MPs), 0D nanoparticles (NPs) and 1D nanowires (NWs), were prepared. It was noticed that the NPs have the smallest support particle size, followed by NWs and MPs. Despite TiO2 NWs having a larger particle size than NPs, the 15% Ni/TiO2 NWs boasted a higher surface area, smaller NiO crystalline and particle size, which resulted in an augmented NiO dispersion. Superior CO2 methanation performance with CO2 conversion, CH4 yield and selectivity of 88.44%, 87.53% and 98.97%, respectively was achieved over 15% Ni/TiO2 NWs. The stability of the TiO2 NWs counterpart over a 40 hours reaction time was the best among the three samples. Spent catalyst analysis also indicated that 15% Ni/TiO2 NWs are highly resistant to catalyst deactivation and coke formation. The prolonged durability was attributed to the 1D wire-like structure, which promoted a higher dispersion of active sites, facilitating an intimate contact between catalyst and reactants. The ameliorated dispersion also mitigates catalyst deactivation via sintering and coke formation. The findings elucidated that the morphology of the catalyst is more influential in enhancing the hydrogenation reaction than the support size.

Promotion effects of alkali metals on iron molybdate catalysts for CO2 catalytic hydrogenation

CO2 hydrogenation is an attractive way to store and utilize carbon dioxide generated by industrial processes, as well as to produce valuable chemicals from renewable and abundant resources. Iron catalysts are commonly used for the hydrogenation of carbon oxides to hydrocarbons. Iron-molybdenum catalysts have found numerous applications in catalysis, but have been never evaluated in the CO2 hydrogenation. In this work, the structural properties of iron-molybdenum catalysts without and with a promoting alkali metal (Li, Na, K, Rb, or Cs) were characterized using X-ray diffraction, hydrogen temperature-programmed reduction, CO2 temperature-programmed desorption, in-situ 57Fe Mossbauer spectroscopy and operando X-ray adsorption spectroscopy. Their catalytic performance was evaluated in the CO2 hydrogenation. During the reaction conditions, the catalysts undergo the formation of an iron (II) molybdate structure, accompanied by a partial reduction of molybdenum and carbidization of iron. The rate of CO2 conversion and product selectivity strongly depend on the promoting alkali metals, and electronegativity was identified as an important factor affecting the catalytic performance. Higher CO2 conversion rates were observed with the promoters having higher electronegativity, while low electronegativity of alkali metals favors higher light olefin selectivity.

An investigation of the Ni/carbonate interfaces on dual function materials in integrated CO2 capture and utilisation cycles

CO2 capture and utilisation (CCU) is a promising strategy to effectively mitigate the adverse greenhouse effects caused by CO2 emissions at an industrial scale. Through a process intensification strategy known as integrated CO2 capture and utilisation (ICCU), CO2 capture and catalytic CO2 conversion can be achieved in a single process with the use of dual function materials (DFMs), which are both CO2 sorbents and CO2 conversion catalysts. Given the significantly different operating conditions of ICCU from conventional catalytic CO2 hydrogenation, the catalytic mechanism of DFMs, especially during CO2 hydrogenation, needs to be thoroughly investigated. In this study, the relationship between the nature of the Ni/carbonate interfaces and the performance of Ni-based DFMs over ICCU cycles is systematically investigated. A series of Ni/alkaline earth carbonate DFMs were synthesised with varying Ca:Mg ratios to simulate different metal-carbonate model interfaces. At 400 °C, CH4 formation with nearly 100% CH4 selectivity was achieved on Ni/CaCO3 over 15 ICCU cycles. In general, Ni/CaCO3 interfaces correspond to higher CO2 conversion and higher CH4 selectivity than Ni/MgCO3 interfaces. Such trend may be attributed to the higher surface basicity of CaO and the higher thermal stability of CaCO3. As a consequence, the hydrogenation of the Ni/CaCO3 interface proceed via the formate pathway, in which carbonates are consecutively converted to surface formates, methoxyl, methyl species and eventually desorb as methane. This reaction model is applicable to the hydrogenation of both surface carbonate and bulk carbonates, although the former proceeds with much faster kinetics. On the weakly alkaline Ni/MgCO3 interface, MgCO3 preferentially decomposes to form gaseous CO2, which is subsequently hydrogenated via the reverse-water-gas-shift pathway, with CO as the key reaction intermediate. Interestingly, in situ infrared spectroscopy shows similar surface significant species during the direct hydrogenation of DFMs and during the conventional catalytic hydrogenation of molecular CO2, suggesting that the catalytic mechanisms during the two operating regimes are highly correlated.

A versatile hybrid catalyst platform of Na/ZnFe2O4 and zeolite for selective hydrocarbon production from CO2 hydrogenation

Catalytic CO2 hydrogenation faces great challenges in both reaction rates and selectivity to desired high-value products. Herein, we present a one-pot reaction platform that converts CO2 into various long-chain hydrocarbons selectively by combining a Na/ZnFe2O4-based catalyst for CO2 activation and carbon–carbon coupling, and a zeolite for fine-tuning the selectivity of desired products by exploiting its shape selectivity. Thus, the Na/ZnFe2O4 catalyst without zeolite produces highly olefinic diesel range hydrocarbons, and a hybrid catalyst with ZSM-5 produces highly aromatic gasoline range hydrocarbons, that with ZSM-11 produces branched kerosene range hydrocarbons, and that with SSZ-13 produces hydrocarbons rich in C2-C4 olefins. In all cases, high CO2 conversions of over 35% and low CO selectivity of near 10% are maintained. Therefore, the hybrid catalyst platform proposed here demonstrates that an elaborate catalyst design enables fine-tuning of the reaction pathway of CO2 hydrogenation to produce selectively versatile value-added hydrocarbons.

Tuning the content of S vacancies in MoS2 by Cu doping for enhancing catalytic hydrogenation of CO2 to methanol

Hydrogenation of CO2 to methanol is one of effective ways to promote "carbon neutrality". The activity of MoS2 as an efficient catalyst for the catalytic hydrogenation of CO2 to methanol is influenced by the content of in-plane S vacancies. Theoretically, the higher the density of in-plane S vacancies is, the better the performance of the catalyst is. In this work, a series of MoS2 nanosheets with different copper (Cu) dopant concentrations were prepared via hydrothermal method. It was found that the highest selectivity of MoS2-catalyzed CO2 hydrogenation to methanol along with the spatial-temporal yield was achieved at the Cu doping of 5%. Compared to the undoped MoS2 catalyst, the increase in methanol selectivity and spatial-temporal yield after doping was 13.37% and 2.27 times, respectively. This was due to the fact that Cu doping multiplied the number of S vacancies on MoS2, which altered the microstructure and chemical properties of the catalyst. However, a further increase in Cu dopant concentration reduced the S vacancy content on the MoS2 substrate, hindering the hydrogenation of the decomposed CO and thus decreasing the methanol yield. Therefore, a new technique to enhance MoS2-catalyzed CO2 hydrogenation to methanol was proposed.

Influence of sodium and potassium proportion on the adsorption of methanol and water on LTA zeolites at high temperature

Catalytic hydrogenation of CO2 or CO, obtained from biomass gasification, is the most used technology to produce renewable methanol. The main problem is that the reactions are controlled by equilibrium, achieving low conversions to methanol, leading to high purification costs and reagent recirculation rates. At 250 °C and 50 bar, the equilibrium conversion of CO2 is around 25%, and methanol selectivity is about 64%. The process can be improved by a sorption-enhanced reaction process (SERP), removing the reaction products in situ and overcoming the equilibrium. To carry out the process, adsorbents with high affinity to the products at high temperatures, like LTA zeolites, are required. Experimental data on methanol and water adsorption at reaction temperatures is quite scarce in the literature, and it is usually assumed that methanol is not adsorbed onto 4A and 3A zeolites. This information is required to design a SERP process with this adsorbent. In this work, the influence of sodium and potassium proportion on the adsorption of methanol and water on LTA zeolites is studied by measuring Henry's adsorption equilibrium constants and reciprocal diffusion time constants. Sodium LTA zeolites (4A) strongly adsorb water and methanol. Potassium-rich LTA zeolites (3A) have higher water/methanol selectivity than sodium-rich LTA zeolites.

Crucial Role of Surface FeOx Components on Supported Fe-Based Nanocatalysts for CO2 Hydrogenation to Light Olefins

Currently, Fe-based catalysts show excellent catalytic performance in the hydrogenation of CO2 to produce light olefins. Despite numerous studies, the identification of the role of catalytically active components over Fe-based catalysts for CO2 hydrogenation is not quite clear. In this work, a series of ZrO2-supported cobalt-doped Fe-based catalysts were fabricated by a microliquid film reactor-assisted coprecipitation method. It was demonstrated that appropriately strong interactions between Fe-containing species and the ZrO2 support in catalyst precursors could facilitate the generation of a defective FeOx component upon reduction treatment and inhibit the carburization of metallic iron during the reaction. Among all Fe-based catalysts, the catalyst bearing a (Co + Fe)/ZrO2 mass ratio of 3:7 and a Co/Fe molar ratio of 1:9 achieved a highest light olefins selectivity of about 38% at 49% CO2 conversion under reaction conditions (i.e., 320 °C, 2.0 MPa, and 4800 mL·gcat–1·h–1), along with a high Fe time yield to light olefins of 9.2 μmolCO2·gFe–1·s–1 and a low CO selectivity of 4.7%. Comprehensive structural characterization and catalytic CO2 hydrogenation experiments clarified that the surface-dominant defect-rich FeOx component as catalytically active species substantially played a crucial role in governing the hydrogenation of CO2, mainly owing to their enhanced adsorption and binding ability for CO2 and the CO intermediate. This study offers a new strategy to design Fe-based catalysts and provides deep insight into the role of iron oxide species for CO2 hydrogenation to produce light olefins.

Reactive ball-milling synthesis of Co-Fe bimetallic catalyst for efficient hydrogenation of carbon dioxide to value-added hydrocarbons

Catalytic hydrogenation of CO2 using renewable hydrogen not only reduces greenhouse gas emissions, but also provides industrial chemicals. Herein, a Co-Fe bimetallic catalyst was developed by a facile reactive ball-milling method for highly active and selective hydrogenation of CO2 to value-added hydrocarbons. When reacted at 320 °C, 1.0 MPa and 9600 mL h−1 gcat−1, the selectivity to light olefin (C2=–C4=) and C5 + species achieves 57.3% and 22.3%, respectively, at a CO2 conversion of 31.4%, which is superior to previous Fe-based catalysts. The CO2 activation can be promoted by the CoFe phase formed by reactive ball milling of the Fe-Co3O4 mixture, and the in-situ Co2C and Fe5C2 formed during hydrogenation are beneficial for the C–C coupling reaction. The initial C–C coupling is related to the combination of CO species with the surface carbon of Fe/Co carbides, and the sustained C–C coupling is maintained by self-recovery of defective carbides. This new strategy contributes to the development of efficient catalysts for the hydrogenation of CO2 to value-added hydrocarbons.

The Function of Hydrotalcite as a Support Material in the Alcohol-Assisted Catalytic CO2 Hydrogenation Reaction.

The traditional CO2 hydrogenation reaction in gas phase always requires harsh reaction conditions to activate CO2 , resulting in huge energy consumption. However, with the assistance of 1-butanol solvent, catalytic CO2 hydrogenation can be proceeded at a mild condition of 170 °C and 30 bars. To further improve the catalytic performance of the widely studied Cu-ZnO-ZrO2 catalyst (CZZ), the catalysts were modified by incorporating hydrotalcite (HTC) as a support material. The addition of HTC significantly improved the copper dispersion and surface area of the catalyst. The performance of CZZ-HTC catalysts was investigated at varying weight percentages of HTC, and all showed higher space-time yield of methanol (STYMeOH ) compared to the commercial catalyst. Notably, CZZ-6HTC exhibited the highest methanol selectivity, further highlighting the beneficial role of HTC as a support material.

Effects of precursor phase distribution on the performance of Cu-based catalysts for direct CO2 conversion to dimethyl ether

Multifunctional Cu-based catalysts with various hydroxyl carbonates as precursors were prepared using hydrothermal and co-precipitation methods for direct catalytic hydrogenation of CO2 to dimethyl ether (DME). By regulating the variable composition and preparation method of the precursor, the phase distribution of the precursor is controlled, and then further affected the structure of the final catalysts. The C-CZA-HT-1/HZ catalyst with a mixture of hydrotalcite-like and aurichalcite precursors prepared by the hydrothermal method possesses uniform dispersion of Cu nanoparticles and excellent catalytic property. The optimized CO2 conversion was 27.6% with the highest DME yield of 12.9% for the C-CZA-HT-1/HZ catalyst. It disclosed that the appropriate Cu–ZnO interaction and oxygen vacancies can create excellent adsorption activation sites for the catalyst, which is essential for achieving high catalytic activity. Moreover, the adsorption and reaction intermediates were obtained by in-situ DRIFTS, and the results revealed that a large amount of formate intermediates could accelerate the conversion. The work provided deep insights into the design of excellent activity catalysts by using controllable hydrotalcite-containing precursors for CO2 catalytic hydrogenation to DME.

Recent advances in catalytic hydrogenation of CO2 into value-added chemicals over oxide–zeolite bifunctional catalysts

Thermo-catalytic CO2 hydrogenation with renewable energy has become one of the promising alternatives to fossil carbon-based routes for the production of bulk chemicals and has been extensively researched in recent years. And the heterogeneous oxide–zeolite (OX–ZEO) bifunctional catalysts have received much attention due to their high product selectivity. However, the need for multifunctional active sites, the complexity of tandem cascade reactions and the difficulty in understanding reaction mechanisms pose significant challenges for the design of effective catalysts. In this review, we present an overview of recent advances in the catalytic hydrogenation of CO2 to value-added products over OX–ZEO bifunctional catalysts, with particular emphasis on the role of the oxide. The nature of the metal oxide, the modification of oxides to improve catalytic performance in CO2 hydrogenation and the reaction mechanisms are discussed. Finally, the current challenges and future perspectives of the catalytic conversion of CO2 to hydrocarbons are briefly presented.

Size-modulated photo-thermal catalytic CO2 hydrogenation performances over Pd nanoparticles

Size of metal nanoparticles significantly influences their catalytic behaviors. However, it is still challenging to obtain monodispersed metal nanoparticles with successively tuned sizes to unveil their size-dependent catalytic performances, especially for photo-thermal catalytic reverse water–gas shift (RWGS) reaction. Herein, a library of Pd nanoparticles of 2.8, 3.4, 4.7, 5.3, 6.3 and 8.1 nm were synthesized and supported on TiO2 for photo-thermal catalytic RWGS reaction. The catalytic activity presented volcano-like dependence on sizes of Pd nanoparticles with 6.3 Pd/TiO2 exhibiting the highest catalytic efficiency. Based on the results of X-ray photoelectron spectroscopic analysis, photo-to-thermal conversion efficiency evaluation and density functional theory (DFT) calculations following the formate (*HCOO) pathway revealed by in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) measurements, the volcano-type tendency in catalytic activity could be attributed to the superposition of size-governed surface electronic properties over Pd nanoparticles.

Cyano group modified graphitic carbon nitride supported Ru nanoparticles for enhanced CO2 methanation

Graphitic carbon nitride (g-C3N4) based materials has been widely used for catalytic CO2 hydrogenation reaction. However, the catalytic activity is restricted due to the barren active sites and the weak ability to activate CO2 for the traditional g-C3N4. We demonstrate here that cyano group modified g-C3N4 supported Ru nanoparticles exhibits high activity and selectivity for CO2 methanation. The introduction of cyano group promotes the formation of medium basic sites for enhanced CO2 adsorption. Meanwhile, the formation of electron-rich Ru nanoparticles with the assistance of cyano group boosts the H2 activation. The synergistic effect of cyano group and Ru nanoparticles improves catalytic performance up to 14 times. Characterizations prove that cyano group with electron-withdrawing properties influences the way of CO2 adsorption via electron transfer and changes the CO2 hydrogenation reaction pathway. This work provides a new insight into the switching of CO2 hydrogenation pathway and enhanced catalytic activity via surface functional groups modification of g-C3N4 based catalyst.

Catalytic Hydrogenation of CO2 to Formate Using Ruthenium Nanoparticles Immobilized on Supported Ionic Liquid Phases (Small 18/2023)

Ruthenium Nanoparticles In article number 2206806 by Alexis Bordet, Walter Leitner, and co-workers, the aqueous phase hydrogenation of CO2 to formate using Ru nanoparticles immobilized on supported ionic liquid phases ([email protected]) is reported. A synergistic enhancement of catalyst activity and productivity is observed for sulfonic acid-functionalized [email protected](SO3H-X) materials, and rationalized by an accelerated desorption of the formate species from the Ru NPs promoted by the presence of ammonium sulfonate species on these catalysts.

Oxide Supported Cobalt Catalysts for CO2 Hydrogenation to Hydrocarbons: Recent Progress

AbstractCarbon capture and utilization represents a promising strategy to meet the global energy and climate goals. Under specific conditions, CO2 catalytic hydrogenation with renewable H2 can transform waste CO2 into a chemical feedstock for added‐value energy carriers and chemicals. CO2‐Fischer–Tropsch synthesis‐based‐hydrocarbons should contribute to the creation of a circular carbon economy with a significant impact on anthropogenic emission into the atmosphere. This review summarizes the progress achieved toward the single‐step hydrogenation of CO2 to long‐chain hydrocarbons over oxide‐supported Co‐based catalysts. Mechanistic aspects are discussed in relation to thermodynamic and kinetic limitations. The main parameters that must be taken into consideration to increase the activity and the selectivity toward compounds of two or more carbon atoms (C2+) are discussed in detail: cobalt active phase, support and metal‐support interfaces, and promoters. Finally, particular focus is dedicated to the role of reducible oxide supports and their surface defects on the activation of CO2, as well as on the regulation and evolution of metal‐support interactions.

Hydroxypyridine/Pyridone Interconversions within Ruthenium Complexes and Their Application in the Catalytic Hydrogenation of CO2

Reaction of a new ligand 6-DiPPon (6-diisopropylphosphino-2-pyridone) with 0.5 equiv of [RuCl2(p-cymene)]2 resulted in the formation of a mixture of [RuCl2(p-cymene)(κ1-P-6-DiPPon)]2 (1) and [RuCl(p-cymene)(κ2-P,N-6-DiPPin)]Cl ([2]Cl) (where 6-DiPPin = 6-diisopropylphosphino-2-hydroxypyridine). The ratio between the two products can be controlled by the nature of the solvent. The similar reaction between 6-DiPPon and [RuCl2(p-cymene)]2 in the presence of AgOTf and Na[BArF24] (where BArF24 = [{3,5-(CF3)2C6H3}4B]-) resulted in the formation of the complexes [RuCl(p-cymene)(κ2-P,N-6-DiPPin)]OTf, ([2]OTf) and [RuCl(p-cymene)(κ2-P,N-6-DiPPin)]BArF24 ([2]BArF24), respectively. Reactions between complex [2]Cl, [2]OTf, or [2]BArF24 and a base (either DBU or NaOMe) resulted in the deprotonation of the hydroxyl functional group to form a novel neutral orange-colored dearomatized complex, 3. The identity of complex 3 was confirmed as [RuCl(p-cymene)(κ2-P,N-6-DiPPon*)], where 6-DiPPon* is the anionic species (6-diisopropylphosphino-2-oxo-pyridinide), which contains the deprotonated moiety. The new 6-DiPPon ligand and its corresponding air stable half-sandwich derivative ruthenium complexes 1, [2]OTf, [2]BArF24, and 3 were all isolated in good yields and fully characterized by spectroscopic and analytical methods. The interconversions between the neutral and anionic forms of the ligands 6-DiPPon, 6-DiPPin, and 6-DiPPon* offer the potential for novel secondary sphere interactions and proton shuttling reactivity. The consequences for this have been explored in the activation of H2 and the subsequent catalytic hydrogenations of CO2 into formate salts in the presence of a base.

Support Nano‐Co/CeO2‐δ Catalyst for CO2 Hydromethanation

AbstractThe large‐scale use of fossil fuels had resulted in massive emission of CO2 and a series of serious environmental problems, which directly threatening human survival and sustainable development. CO2 is also the abundant carbon resource in C1 family. CO2 catalytic hydrogenation to CH4 is one of the effective ways to ultilize CO2 with low energy and high efficiency, which has been widely concerned in recent years. Suppoted nano‐Co/CeO2‐δ catalysts were prepared and evaluated their CO2 hydrogenation performances. XRD, H2‐TPR, H2‐TPD and CO2‐TPD had been conducted to study the physicochemical properties of the prepared Co/CeO2‐δ catalysts. The Co loading significantly affects the physicochemical properties and CO2 hydrogenation performances. The active metal Co species were highly diepersed on the CeO2 support surface. The number of active metal Co species, which formed by H2 reduction, increased with the increasing of Co loading. And the ability to adsorb and activate the reactant H2 and CO2 molecules was also enhanced, which effectively promoted the CO2 hydrogenation performances. Among of the studied Co/CeO2‐δ catalysts, the CoCe09 catalyst with Co loading of 9 % showed the best CO2 catalytic hydrogenation activity. In the reaction temperature of 240–400 °C, the CO2 conversion and CH4 selectivity follow the order: CoCe01<CoCe03<CoCe05<CoCe11<CoCe09. At 400 °C, the CO2 conversion increases from 30.1 % (CoCe01) to 59.2 % (CoCe09).

Alkoxide-Decorated Copper Nanoparticles on Amidine-Modified Polymers as Hydrogenation Catalysts for Enabling H2 Heterolysis

Direct formation of Cu nanoparticles was accomplished on an amidine- and guanidine-functionalized polymer (polystyrene-bound 1,8-diazabicyclo[5.4.0]undec-7-ene (PS-DBU) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (PS-TBD), respectively) by thermal treatment of Cu(acac)2 (acac = acetylacetonato) in methanol under pressurized H2. The immobilized structure was characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES), elemental analysis, and microscopic analysis. X-ray photoelectron spectroscopy (XPS) data indicated that the nanoparticles consisted of Cu(0) and oxygenated Cu(I). The Cu(0)/Cu(I) ratio was determined by X-ray absorption spectroscopy. In particular, X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) studies indicated the inclusion of alkoxides bound to Cu nanoparticles. Further 13C-labeled experiments allowed us to identify the Cu methoxide species by solid-state 13C nuclear magnetic resonance (NMR). A series of alkoxide-incorporated Cu nanoparticles were proven to facilitate H2 heterolysis and were applied in the catalytic hydrogenation of CO2 to formate salts in the presence of a nitrogen base. The catalytic activity increased with decreased mean particle size and increased Cu(I) content, indicating that the Cu(I) alkoxide species played an indispensable role in hydrogenation. The combination of Cu/PS-DBU and 2-tert-butyl-1,1,3,3-tetramethylguanidine (BTMG) achieved a maximum turnover number of 2450 at 100 °C without leaching or aggregation of the nanosized catalysts.

Ir-CoO Active Centers Supported on Porous Al2 O3 Nanosheets as Efficient and Durable Photo-Thermal Catalysts for CO2 Conversion.

Photo-thermal catalytic CO2 hydrogenation is currently extensively studied as one of the most promising approaches for the conversion of CO2 into value-added chemicals under mild conditions; however, achieving desirable conversion efficiency and target product selectivity remains challenging. Herein, the fabrication of Ir-CoO/Al2 O3 catalysts derived from Ir/CoAl LDH composites is reported for photo-thermal CO2 methanation, which consist of Ir-CoO ensembles as active centers that are evenly anchored on amorphous Al2 O3 nanosheets. A CH4 production rate of 128.9 mmol gcat⁻ 1 h⁻1 is achieved at 250 °C under ambient pressure and visible light irradiation, outperforming most reported metal-based catalysts. Mechanism studies based on density functional theory (DFT) calculations and numerical simulations reveal that the CoO nanoparticles function as photocatalysts to donate electrons for Ir nanoparticles and meanwhile act as "nanoheaters" to effectively elevate the local temperature around Ir active sites, thus promoting the adsorption, activation, and conversion of reactant molecules. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) demonstrates that illumination also efficiently boosts the conversion of formate intermediates. The mechanism of dual functions of photothermal semiconductors as photocatalysts for electron donation and as nano-heaters for local temperature enhancement provides new insight in the exploration for efficient photo-thermal catalysts.