Active Heterogeneous Ru Nanocatalysts for CO2 Hydrogenation Reaction

Influence of the calcination conditions of the support on the activity of ruthenium-encapsulated porous hollow silica sphere catalysts for hydrogenation of carbon dioxide into formic acid

The present study investigated the influence of the calcination conditions of porous hollow silica spheres on the activity of a ruthenium-encapsulated porous hollow silica sphere catalyst for hydrogenation of carbon dioxide into formic acid. The hollow spheres were prepared at various calcination temperatures in air or in an argon flow. The amount of residual carbon content in the ruthenium-encapsulated hollow silica sphere catalysts increased with a decrease in the calcination temperature of the hollow silica sphere supports in air. Energy dispersive X-ray spectroscopy (EDS) and thermogravimetric (TG) analyses revealed that cetyltrimethylammonium bromide (CTAB) preferentially decomposed at calcination temperatures of up to 673 K, and most of the CTAB and carbon templates decomposed with the collapse of the hollow sphere catalyst particles in the catalysts calcined at 873 K. Moreover, the highest amounts of residual CTAB and carbon templates were found in the catalysts calcined in the argon flow. Differential thermal analysis (DTA), transmission electron microscopy (TEM), nitrogen sorption and X-ray diffraction (XRD) measurements showed that active ruthenium species were highly dispersed in the hollow spheres calcined in air, while a small amount of active ruthenium species with low dispersion were supported on the hollow spheres calcined in the argon flow. The catalyst calcined at 473 K exhibited the highest turnover number (TON) for formic acid formation (350 mol-HCOOH per mol-Ru), suggesting that the catalysts exhibited high activity not only owing to the high dispersion of the active species but also owing to the effective conduction of reaction heat by residual carbon species originating from CTAB in the nanospaces of the hollow spheres' shells.

Advanced zeolite and ordered mesoporous silica-based catalysts for the conversion of CO2 to chemicals and fuels

For many years, capturing, storing or sequestering CO₂ from concentrated emission sources or from air has been a powerful technique for reducing atmospheric CO₂. Moreover, the use of CO₂ as a C1 building block to mitigate CO₂ emissions and, at the same time, produce sustainable chemicals or fuels is a challenging and promising alternative to meet global demand for chemicals and energy. Hence, the chemical incorporation and conversion of CO₂ into valuable chemicals has received much attention in the last decade, since CO₂ is an abundant, inexpensive, nontoxic, nonflammable, and renewable one-carbon building block. Nevertheless, CO₂ is the most oxidized form of carbon, thermodynamically the most stable form and kinetically inert. Consequently, the chemical conversion of CO₂ requires highly reactive, rich-energy substrates, highly stable products to be formed or harder reaction conditions. The use of catalysts constitutes an important tool in the development of sustainable chemistry, since catalysts increase the rate of the reaction without modifying the overall standard Gibbs energy in the reaction. Therefore, special attention has been paid to catalysis, and in particular to heterogeneous catalysis because of its environmentally friendly and recyclable nature attributed to simple separation and recovery, as well as its applicability to continuous reactor operations. Focusing on heterogeneous catalysts, we decided to center on zeolite and ordered mesoporous materials due to their high thermal and chemical stability and versatility, which make them good candidates for the design and development of catalysts for CO₂ conversion. In the present review, we analyze the state of the art in the last 25 years and the potential opportunities for using zeolite and OMS (ordered mesoporous silica) based materials to convert CO₂ into valuable chemicals essential for our daily lives and fuels, and to pave the way towards reducing carbon footprint. In this review, we have compiled, to the best of our knowledge, the different reactions involving catalysts based on zeolites and OMS to convert CO₂ into cyclic and dialkyl carbonates, acyclic carbamates, 2-oxazolidones, carboxylic acids, methanol, dimethylether, methane, higher alcohols (C₂₊OH), C₂₊ (gasoline, olefins and aromatics), syngas (RWGS, dry reforming of methane and alcohols), olefins (oxidative dehydrogenation of alkanes) and simple fuels by photoreduction. The use of advanced zeolite and OMS-based materials, and the development of new processes and technologies should provide a new impulse to boost the conversion of CO₂ into chemicals and fuels.

Highly selective hydrogenation of dimethyl oxalate to methyl glycolate and ethylene glycol over an amino-assisted Ru-based catalyst

A Ru/NH₂-MCM-41 catalyst was prepared via a coordination-assisted strategy for chemoselective hydrogenation of dimethyl oxalate with a high selectivity of methyl glycolate (ca. 100%) and ethylene glycol (>90%) at reaction temperatures of 343 K and 433 K, respectively. The amino groups help to anchor and form stable electron-rich Ru active sites, which accounts for the excellent CO bond activation and hydrogenation selectivity.

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 presence of a strong base. But due to the use of toxic CO molecule and easy availability of CO2 molecule 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:

To develop reaction protocol to achieve easy CO2 hydrogenation to formic acid using 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), namely Ru@TiO2@IL and Ru@TiO2. We are reporting the application NR2 (R= CH3) containing imidazolium- based ionic liquids not only to achieve a good reaction rate but also to 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,Ndimethylaminoethyl)- 2-methylimidazolium trifluoromethanesulfonate ([DAMI][TfO]), 1,3-di(N,Ndimethylaminoethyl)- 2-methylimidazolium bis (trifluoromethylsulfonyl) imide ([DAMI][NTf2]) and 1-butyl-3-methylimidazolium chloride ionic liquids which were synthesized as per the reported procedure.

Results:

We easily developed two types 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 and functionalized [DAMI] [TfO] ionic liquid.

Conclusion:

Here we demonstrated the preparation and characterization of TiO2 supported Ru nanoparticles with and without ionic liquid. 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. During the optimization, we also noticed the significant effect of functionalized [DAMI] [TfO] ionic liquid and water to improve the formic acid yield. Lastly, we also checked the stability of the catalyst by recycling the same till the 7th run.

Selective formation of formic acid from biomass-derived glycolaldehyde with supported ruthenium hydroxide catalysts

Ceria-supported ruthenium hydroxide catalysts, Ru(OH)_x/CeO₂, with micro- and nanoparticle supports were applied for selective aerobic oxidation of glycolaldehyde (GAD) to formic acid (FA) in water under mild and base-free conditions.