One-Pot Synthesis of Ni0.05Ce0.95O2−δ Catalysts with Nanocubes and Nanorods Morphology for CO2 Methanation Reaction and in Operando DRIFT Analysis of Intermediate Species

The valorization of CO2 via renewable energy sources allows one to obtain carbon-neutral fuels through its hydrogenation, like methane. In this study, Ni0.05Ce0.95O2−δ catalysts were prepared using a simple one-pot hydrothermal method yielding nanorod and nanocube particles to be used for the methanation reaction. Samples were characterized by XRD, BET, TEM, H2-TPR, and H2-TPD experiments. The catalytic activity tests revealed that the best performing catalyst was Ni0.05Ce0.95O2−δ, with nanorod morphology, which gave a CO2 conversion of 40% with a selectivity of CH4 as high as 93%, operating at 325 °C and a GHSV of 240,000 cm3 h−1 g−1. However, the lower activation energy was found for Ni0.05Ce0.95O2−δ catalysts with nanocube morphology. Furthermore, an in operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis was performed flowing CO2:H2 or CO:H2 mixture, showing that the main reaction pathway, for the CO2 methanation, is the direct hydrogenation of formate intermediate.

Selectivity descriptors for the direct hydrogenation of CO2 to hydrocarbons during zeolite-mediated bifunctional catalysis

Cascade processes are gaining momentum in heterogeneous catalysis. The combination of several catalytic solids within one reactor has shown great promise for the one-step valorization of C1-feedstocks. The combination of metal-based catalysts and zeolites in the gas phase hydrogenation of CO2 leads to a large degree of product selectivity control, defined mainly by zeolites. However, a great deal of mechanistic understanding remains unclear: metal-based catalysts usually lead to complex product compositions that may result in unexpected zeolite reactivity. Here we present an in-depth multivariate analysis of the chemistry involved in eight different zeolite topologies when combined with a highly active Fe-based catalyst in the hydrogenation of CO2 to olefins, aromatics, and paraffins. Solid-state NMR spectroscopy and computational analysis demonstrate that the hybrid nature of the active zeolite catalyst and its preferred CO2-derived reaction intermediates (CO/ester/ketone/hydrocarbons, i.e., inorganic-organic supramolecular reactive centers), along with 10 MR-zeolite topology, act as descriptors governing the ultimate product selectivity.

Combined Spectroscopic and Computational Study of Nitrobenzene Activation on Non-Noble Metals-Based Mono- and Bimetallic Catalysts

In this paper, substituted anilines are industrially obtained by direct hydrogenation of nitroaromatic compounds with molecular H2 using metals as catalysts. Previous theoretical studies proposed that the mechanism of the reaction depends on the nature of the metal used as a catalyst, and that rationally designed bimetallic materials might show improved catalytic performance. Herein, we present IR spectroscopic studies of nitrobenzene interactions with monometallic Ni/SiO2, Cu/SiO2 and Pd/SiO2, and with bimetallic CuNi/SiO2 and CuPd/SiO2 catalysts, both in the absence and presence of H2, combined with density functional theory (DFT) calculations on selected bimetallic NiCu(111) and PdCu(111) models. The results obtained experimentally confirm that the reaction mechanism on non-noble metals such as Ni proceeds through N-O bond dissociation, generating nitrosobenzene intermediates, while, on noble metals, such as Pd, H-attack is necessary to activate the NO bond. Moreover, a bimetallic CuPd/SiO2 catalyst with a Pd enriched surface is prepared that exhibits an enhanced H2 dissociation ability and a particular reactivity at the boundary between the two metals.

Thermodynamic Analysis of Methanol Synthesis via CO2 Hydrogenation Reaction

The most inspiring opportunity to reduce greenhouse gas emissions is direct hydrogenation of CO2 into a commodity of products, which is also an appealing choice for generating renewable energy. CO2 hydrogenation can yield methanol which has a broad range of applications. In the present study, a thermodynamic feasibility analysis of the CO2 hydrogenation reaction is carried out using the Aspen Plus tool. CO2 hydrogenation to methanol, reverse-water-gas-shift (RWGS), and methanol decomposition reactions were considered in this analysis. The effect of different parameters such as temperature (ranging from 50 to 500°C), pressures (ranging from 1 bar to 50 bar), and CO2:H2 molar ratio (ranging from 1:3 to 1:20) on methanol yield has been investigated. The Aspen predicted data is compared with the fixed-bed reactor experimental data. High pressure and low-temperature conditions are found to be the favourable option for a higher value of methanol yield. The CO2 conversion and CH3OH selectivity are favourable when the H2/CO2 molar ratio is greater than 3. A substantial gap between the Aspen predicted equilibrium conversion of CO2 and the experimental value of CO2 conversion is observed in the study.

Biogas Reforming as a Precursor for Integrated Algae Biorefineries: Simulation and Techno-Economic Analysis

Biogas is a significant by-product produced in algae processing and may be used for many different applications, not only as a renewable energy carrier but also as a chemical intermediate in integrated algae-based biorefineries. In this work, the reforming of biogas to H2/CO2 mixtures (referred to as SynFeed) as feed for the direct hydrogenation of CO2 to methanol is investigated. Two conventional processes, namely steam methane and autothermal reforming, with upstream CO2 separation from raw biogas are compared to novel concepts of direct biogas bi- and tri-reforming. In addition, downstream CO2 separation from SynFeed using the commercial Selexol process to produce pure H2 and CO2 is considered. The results show that upstream CO2 separation with subsequent steam methane reforming is the most economic process, costing 142.48 €/tSynFeed, and taking into consideration the revenue from excess hydrogen. Bi-reforming is the most expensive process, with a cost of 413.44 €/tSynFeed, due to the high demand of raw biogas input. Overall, SynFeed from biogas is more economical than SynFeed from CO2 capture and water electrolysis (464 €/tSynFeed), but is slightly more expensive than using natural gas as an input (107 €/SynFeed). Carbon capture using Selexol comes with costs of 22.58–27.19 €/tCO2, where approximately 50% of the costs are derived from the final CO2 compression.

Direct Synthesis of Formic acid from Carbon Dioxide by Hydrogenation over Ruthenium Metal Doped Titanium Dioxide Nanoparticles in Functionalized Ionic Liquid

Background: Presently worldwide manufacturing of formic acid follows the permutation of methanol and carbon monoxide in the presence of a strong base. But due to the use of toxic CO molecules and easy availability of CO2 molecules in the atmosphere, most of the research has been shifted from the conventional method of formic acid synthesis to direct hydrogenation of CO2 gas using different homogenous and heterogeneous catalysts. Objective: The study aims to develop a reaction protocol to achieve easy CO2 hydrogenation to formic acid using an Ionic liquid reaction medium. Methods: We used the sol-gel method followed by calcination (over 250oC for 5 hours) to synthesize two types of ruthenium metal-doped TiO2 nanoparticles (with and without ionic liquids) Ru@TiO2@IL and Ru@TiO2. We report the application NR2 (R= CH3) containing imidazolium-based ionic liquids to achieve a good reaction rate and get agglomeration free ruthenium metal-doped TiO2 nanoparticles along with easy product isolation due to the presence of NR2 (R= CH3) functionality in ionic liquid structure. We synthesized various NR2 (R= CH3) functionalized ionic liquids such as 1-Butyl-3-methylimidazolium Chloride, 1,3-di(N,N-dimethylaminoethyl)-2-methylimidazolium trifluoromethane sulfonate ([DAMI][TfO]), 1,3-di(N,N-dimethylaminoethyl)-2-methylimidazolium bis (trifluoromethylsulfonyl) imide ([DAMI][NTf2]) and 1-butyl-3-methylimidazolium chloride ionic liquids were synthesized as per the reported procedure. Results: We quickly developed two typed of Ru metal-doped TiO2 nanoparticles using the sol-gel method. After calcination, both Ru@TiO2@IL (3.2 wt% Ru), and Ru@TiO2 (1.7 wt% Ru) materials were characterized by XRD, FTIR, TEM, ICP-AES, EDS, and XANES analysis. After understanding the correct structural arrangement of Ru metal over TiO2 support, we utilized both Ru@TiO2@IL (3.2 wt% Ru) and Ru@TiO2 (1.7 wt% Ru) the materials as a catalyst for direct hydrogenation of CO2 in the presence of water. We functionalized [DAMI] [TfO] ionic liquid. Conclusion: After understanding the correct morphology and physiochemical analysis of Ru@TiO2@IL (3.2 wt% Ru), and Ru@TiO2 (1.7 wt% Ru) catalysts, we examined their application in CO2 reduction and formic acid synthesis. Here we demonstrated the preparation and characterization of TiO2 supported Ru nanoparticles with and without ionic liquid. We also noticed the significant effect of functionalized [DAMI] [TfO] ionic liquid and water to improve the formic acid yield during the optimization. Last, we also checked the stability of the catalyst by recycling the same till the 7th run.

Synthesis and Characterization of Nickel(II) Homogeneous and Supported Complexes for the Hydrogenation of Furfural to Furfuryl Alcohol

Nickel(II) complexes have been synthesized and characterized using nuclear magnetic resonance (NMR), infrared spectroscopy, high resolution mass spectroscopy, and elemental analysis. The complexes were evaluated as pre-catalysts in the direct hydrogenation of furfural to furfuryl alcohol. The pre-catalysts C1 and C4 gave higher furfural conversion (97% and 96%, respectively), as a result, they were also evaluated in the transfer hydrogenation of furfural using formic acid as the hydrogen source where higher furfural conversion (93%) was obtained and selectivity (100%) toward the formation of furfuryl alcohol at 4 h. The catalyst C1 was recycled three times with and it was observed that the catalytic activity might be due to a mixture of both molecular catalysis and nanoparticles, as evidenced by the decrease in activity in mercury poisoning experiments. The hydrogenation reactions were also extended to alpha-β unsaturated substrates and were selective toward saturation of the carbonyl functionality over alkene groups.

Gallium nitride catalyzed the direct hydrogenation of carbon dioxide to dimethyl ether as primary product

The selective hydrogenation of CO2 to value-added chemicals is attractive but still challenged by the high-performance catalyst. In this work, we report that gallium nitride (GaN) catalyzes the direct hydrogenation of CO2 to dimethyl ether (DME) with a CO-free selectivity of about 80%. The activity of GaN for the hydrogenation of CO2 is much higher than that for the hydrogenation of CO although the product distribution is very similar. The steady-state and transient experimental results, spectroscopic studies, and density functional theory calculations rigorously reveal that DME is produced as the primary product via the methyl and formate intermediates, which are formed over different planes of GaN with similar activation energies. This essentially differs from the traditional DME synthesis via the methanol intermediate over a hybrid catalyst. The present work offers a different catalyst capable of the direct hydrogenation of CO2 to DME and thus enriches the chemistry for CO2 transformations.