Miklos Czaun

Carbon Dioxide Capture from the Air Using a Polyamine Based Regenerable Solid Adsorbent

Easy to prepare solid materials based on fumed silica impregnated with polyethylenimine (PEI) were found to be superior adsorbents for the capture of carbon dioxide directly from air. During the initial hours of the experiments, these adsorbents effectively scrubbed all the CO(2) from the air despite its very low concentration. The effect of moisture on the adsorption characteristics and capacity was studied at room temperature. Regenerative ability was also determined in a short series of adsorption/desorption cycles.

Air as the renewable carbon source of the future: an overview of CO2 capture from the atmosphere

The burning of our diminishing fossil fuel reserves is accompanied by a large anthropogenic CO2 release, which is outpacing natures CO2 recycling capability, causing significant environmental harm. Much is being done to avert this crisis including more efficient technology for usage, savings and replacing carbon fuels with alternatives whenever feasible. The capture of CO2 followed by sequestration (CCS) into geologic formation or under the seas has also been proposed and in some cases implemented. Carbon capture and recycling (CCR) to fuels and materials is another promising approach. At first, capturing carbon dioxide from concentrated sources such as fossil fuel burning power plants, industrial plants and natural sources might be the most practical. However, the capture of CO2 from the atmosphere is also technically feasible despite its low concentration (∼390 ppm) and presents even some benefits compared to point source CO2 capture. The present article reviews methods developed for the capture of CO2 directly from the air as well as their advantages and drawbacks. While strong bases such as sodium hydroxide and potassium hydroxide could be used, their regeneration is energy intensive, requiring high temperatures. Amines either physically or chemically immobilized on solid supports require much lower temperatures for their regeneration and are therefore promising candidates.

Conversion of CO2 from Air into Methanol Using a Polyamine and a Homogeneous Ruthenium Catalyst

A highly efficient homogeneous catalyst system for the production of CH3OH from CO2 using pentaethylenehexamine and Ru-Macho-BH (1) at 125-165 °C in an ethereal solvent has been developed (initial turnover frequency = 70 h(-1) at 145 °C). Ease of separation of CH3OH is demonstrated by simple distillation from the reaction mixture. The robustness of the catalytic system was shown by recycling the catalyst over five runs without significant loss of activity (turnover number > 2000). Various sources of CO2 can be used for this reaction including air, despite its low CO2 concentration (400 ppm). For the first time, we have demonstrated that CO2 captured from air can be directly converted to CH3OH in 79% yield using a homogeneous catalytic system.

Bi-reforming of Methane from Any Source with Steam and Carbon Dioxide Exclusively to Metgas (CO–2H2) for Methanol and Hydrocarbon Synthesis

A catalyst based on nickel oxide on magnesium oxide (NiO/MgO) thermally activated under hydrogen is effective for the bi-reforming with steam and CO(2) (combined steam and dry reforming) of methane as well as natural gas in a tubular flow reactor at elevated pressures (5-30 atm) and temperatures (800-950 °C). By adjusting the CO(2)-to-steam ratio in the gas feed, the H(2)/CO ratio in the produced syn-gas could be easily adjusted in a single step to the desired value of 2 for methanol and hydrocarbon synthesis.

Hydrogen Generation from Formic Acid Decomposition by Ruthenium Carbonyl Complexes. Tetraruthenium Dodecacarbonyl Tetrahydride as an Active Intermediate

The present Minireview covers the formation and the structural characterization of noble metal carbonyl and hydrido carbonyl complexes, with particular emphasis on ruthenium complexes using formic acid as a carbonyl and hydride source. The catalytic activity of these organometallic compounds for the decarboxylation of formic acid, a potential hydrogen storage material, is also reviewed. In addition, the first preparation of [Ru(4)(CO)(12)H(4)] from RuCl(3) and formic acid as well as the catalytic activity of [Ru(4)(CO)(12)H(4)] for the decomposition of formic acid to hydrogen and carbon dioxide are presented.

Easily Regenerable Solid Adsorbents Based on Polyamines for Carbon Dioxide Capture from the Air

Adsorbents prepared easily by impregnation of fumed silica with polyethylenimine (PEI) are promising candidates for the capture of CO2 directly from the air. These inexpensive adsorbents have high CO2 adsorption capacity at ambient temperature and can be regenerated in repeated cycles under mild conditions. Despite the very low CO2 concentration, they are able to scrub efficiently all CO2 out of the air in the initial hours of the experiments. The influence of parameters such as PEI loading, adsorption and desorption temperature, particle size, and PEI molecular weight on the adsorption behavior were investigated. The mild regeneration temperatures required could allow the use of waste heat available in many industrial processes as well as solar heat. CO2 adsorption from the air has a number of applications. Removal of CO2 from a closed environment, such as a submarine or space vehicles, is essential for life support. The supply of CO2-free air is also critical for alkaline fuel cells and batteries. Direct air capture of CO2 could also help mitigate the rising concerns about atmospheric CO2 concentration and associated climatic changes, while, at the same time, provide the first step for an anthropogenic carbon cycle.

Single Step Bi-reforming and Oxidative Bi-reforming of Methane (Natural Gas) with Steam and Carbon Dioxide to Metgas (CO-2H2) for Methanol Synthesis: Self-Sufficient Effective and Exclusive Oxygenation of Methane to Methanol with Oxygen

Catalysts based on suitable metal oxide supports, such as NiO/MgO and CoO/MgO, were shown to be active for single step bi-reforming, the combined steam and dry reforming of methane or natural gas with H2O and CO2 exclusively to metgas (CO-2H2) for efficient methanol synthesis. Reactions were carried out in a tubular flow reactor under pressures up to 42 bar at 830-910 °C. Using a CH4 to steam to CO2 ratio of ∼3:2:1 in the gas feed, the H2/CO ratio of 2:1 was achieved, which is desired for subsequent methanol synthesis. The needed 2/1 steam/CO2 feed ratio together with the reaction heat for the endothermic bi-reforming can be conveniently obtained by the complete combustion of a quarter part of the overall used methane (natural gas) with oxygen of the air (oxidative bi-reforming). Complete combustion of a part of methane followed by bi-reforming leads to the production of metgas (H2/CO in 2:1 mol ratio) for self-sufficient exclusive methanol synthesis. The long sought after but elusive efficient and selective oxygenation of methane to methanol is thus achieved in an effective and economic way without any oxidation byproduct formation according to CH4 + 1/2O2 → CH3OH.

Amine-free reversible hydrogen storage in formate salts catalyzed by ruthenium pincer complex without pH control or solvent change.

Due to the intermittent nature of most renewable energy sources, such as solar and wind, energy storage is increasingly required. Since electricity is difficult to store, hydrogen obtained by electrochemical water splitting has been proposed as an energy carrier. However, the handling and transportation of hydrogen in large quantities is in itself a challenge. We therefore present here a method for hydrogen storage based on a CO2 (HCO3 (-) )/H2 and formate equilibrium. This amine-free and efficient reversible system (>90 % yield in both directions) is catalyzed by well-defined and commercially available Ru pincer complexes. The formate dehydrogenation was triggered by simple pressure swing without requiring external pH control or the change of either the solvent or the catalyst. Up to six hydrogenation-dehydrogenation cycles were performed and the catalyst performance remained steady with high selectivity (CO free H2 /CO2 mixture was produced).

A novel approach to magneto-responsive polymeric gels assisted by iron nanoparticles as nano cross-linkers

A new route for the preparation of magneto-responsive polymeric gels involving iron nanoparticles as nano cross-linkers has been described.

CO2 capture by amines in aqueous media and its subsequent conversion to formate with reusable ruthenium and iron catalysts

Conversion of carbon dioxide (CO2) captured from industrial sources (e.g. flue gas of power plants) or even from ambient air to value-added chemicals/fuels through CO2 capture and utilization (CCU) as a possible strategy to mitigate anthropogenic CO2 emissions to the atmosphere is proposed. In this context, combining the CO2 capture and utilization steps to generate fuels instead of going through the intermediate desorption and compression of captured CO2 has started to attract considerable interest as a way to lower the energy demand for the CO2 recovery processes involved in usual carbon capture and storage/sequestration approach. The main focus of this study is CO2 capture in aqueous amine solutions and conversion of the in situ formed ammonium carbamate/bicarbonate/carbonate to ammonium formate. The amines selected for this process served the dual purpose of capturing CO2 and stabilizing the formate product. The captured CO2 was selectively converted to formate (up to 95% yield) using, among others, superbases, in the presence of Ru- and Fe-based pincer complexes under moderate reaction conditions (50 bar H2 at 55 °C). By performing a biphasic reaction (water/Me-THF), the catalyst was recycled for five consecutive cycles and a TON > 7000 was obtained for the formation of ammonium formate from captured CO2. Overall, a green and straightforward approach to produce formate from captured CO2 is presented here.