No abstract

Due to the increasing CO 2 concentration in the atmosphere, contemporary research has focused on ways to slow or stop this trend. CO 2 capture has attracted attention due to the potential to trap and sequester large amounts of CO 2 from concentrated sources such as power plants. Traditional technologies in capturing CO 2 include absorption by aqueous amines. 1 However, utilization of this process is energy intensive and expensive when used for large volumes of dilute gas, such as flue gas. 2 This is primarily due to the high heat capacity of water and use of temperature swings to induce CO 2 desorption. Many types of amine-modified silica materials have been reported (e.g., amine-tethered silica materials, 3 amines impregnated into porous silicas, 4,5 etc.) as possible solid adsorbents for CO 2 capture from flue gas streams. However, these materials generally suffer from low CO 2 capacities or lack stability over many cycles, especially when amines are physisorbed onto the support. Therefore, it is advantageous to synthesize an organic/ inorganic hybrid amine-tethered silica material with high amine loadings (>6 mmol/g) capable of reversibly binding CO 2 rather than employing physisorbed, impregnated adsorbents that may be unstable after several cycles. Here we describe the synthesis of a covalently tethered hyperbranched aminosilica (HAS) material 6-8 capable of binding CO 2 reversibly from simulated flue gas, and we compare its CO 2 capacity with those of other reported solid amine adsorbents (Scheme 1). We conceived of these HAS materials as practical CO 2 adsorbents due to their simple synthesis, covalent inorganic-organic linkage, and low cost. The HAS material has the highest fully regenerable CO 2 capacity for a covalently supported adsorbent under simulated flue gas conditions. The synthesis of HAS was performed via a one-step reaction between aziridine and the silica surface. 6 As previously reported on silica wafers, the surface silanols initiated aziridine polymerization off the surface. 6 Due to low surface areas, hybrid aminosilica materials constructed on silica wafers are impractical adsorbents. However, the formation of hybrid aminosilicas on high surface area mesoporous silica materials 7,8 can lead to materials capable of reversibly binding CO 2 with substantial capacities (>2 mmol CO 2 / g). The aziridine monomer was added to SBA-15 dispersed in a toluene solution with catalytic amounts of acetic acid and stirred at room temperature in a glass pressure reaction vessel. The resulting HAS material (SBA-HA) was washed extensively to remove physisorbed aziridine or unbound oligomer from the surface. The organic loading of the grafted hybrid aminosilica used here was determined via elemental analysis as 7.0 mmol N/g material.For these studies, the hybrid aminosilica was uniformly dispersed in sand and tested in a fixed bed flow system. The adsorbent/sand mixture allowed for decreased heat effects and reproducible flow through the bed. The SBA-HA material was analyzed for CO 2 capture at 25°C and 75...

Plasma catalysis is gaining increasing interest for various gas conversion applications, such as CO2 conversion into value-added chemicals and fuels, CH4 activation into hydrogen, higher hydrocarbons or oxygenates, and NH3 synthesis. Other applications are already more established, such as for air pollution control, e.g. volatile organic compound remediation, particulate matter and NOx removal. In addition, plasma is also very promising for catalyst synthesis and treatment. Plasma catalysis clearly has benefits over ‘conventional’ catalysis, as outlined in the Introduction. However, a better insight into the underlying physical and chemical processes is crucial. This can be obtained by experiments applying diagnostics, studying both the chemical processes at the catalyst surface and the physicochemical mechanisms of plasma-catalyst interactions, as well as by computer modeling. The key challenge is to design cost-effective, highly active and stable catalysts tailored to the plasma environment. Therefore, insight from thermal catalysis as well as electro- and photocatalysis is crucial. All these aspects are covered in this Roadmap paper, written by specialists in their field, presenting the state-of-the-art, the current and future challenges, as well as the advances in science and technology needed to meet these challenges.

Nonthermal plasma-driven catalysis is an emerging subfield of heterogeneous catalysis that is particularly promising for the chemical transformation of hard-to-activate molecules (e.g., N 2 , CO 2 , CH 4 ). In this Review, we illustrate this promise of plasmaenhanced catalysis, focusing on the ammonia synthesis and methane dry reforming reactions, two reactions that have received wide attention and that illustrate the potential for plasma excitations to mitigate kinetic and thermodynamic obstacles to chemical conversions. We highlight how plasma activation of reactants can provide access to overall reaction rates, conversions, product yields, and/or product distributions unattainable by thermal catalysis at similar temperatures and pressures. Particular emphasis is given to efforts aimed at discerning the underlying mechanisms at play in these systems. We discuss opportunities for and challenges to the advancement of the field.