Minimizing energy demand and environmental impact for sustainable NH3 and H2O2 production—A perspective on contributions from thermal, electro-, and photo-catalysis

There is an urgent need to provide adequate and sustainable supplies of water and food to satisfy the demand of an increasing population. Catalysis plays important roles in meeting these needs by facilitating the synthesis of hydrogen peroxide that is used in water decontamination and chemicals production, and ammonia that is used as fertilizer. However, these chemicals are currently produced with processes that are either very energy-intensive or environmentally unfriendly. This article offers the perspectives of the challenges and opportunities in the production of these chemicals, focusing on the roles of catalysis in more sustainable, alternative production methods that minimize energy consumption and environmental impact. While not intended to be a comprehensive review, the article provides a critical review of selected literature relevant to its objectives, discusses areas needed for further research, and potential new directions inspired by new developments in related fields. For each chemical, production by thermal, electro-, and photo-excited processes are discussed. Problems that are common to these approaches and their differences are identified and possible solutions suggested

CO₂ Capture by Porous Hyper-Cross-Linked Aromatic Polymers Synthesized Using Tetrahedral Precursors

Low-cost synthesis of porous hyper-cross-linked aromatic polymers (PHAPs) was achieved via the FeCl₃-catalyzed Friedel–Crafts alkylation reaction between tetraphenylsilane or tetraphenylgermanium as a building block and formaldehyde dimethylacetal as a cross-linker. The synthesized polymers were chemically and thermally stable and exhibited high surface areas of up to 1137 m² g^–1 (PHAP-1) and 1059 m² g^–1 (PHAP-2). The adsorption isotherms of the PHAPs revealed a high CO₂ adsorption capacity (104.3–114.4 mg g^–1) with an isosteric heat of adsorption in the range 26.5–27.3 kJ mol^–1 and a moderate CH₄ adsorption capacity (12.6–13.8 mg g^–1) at 273 K and 1 bar. The PHAP networks also exhibited high CO₂/N₂ and CO₂/CH₄ relativities of 29.3–34.2 and 11.3–12.5, respectively, at 273 K

Hydroxylamine-Anchored Covalent Aromatic Polymer for CO₂ Adsorption and Fixation into Cyclic Carbonates

Hydroxylamine-anchored covalent aromatic polymer (CAP-DAP) was synthesized from <i>p</i>-terphenyl and 1,3,5-benzene tricarbonyl chloride, followed by subsequent functionalization with 1,3-diamino-2-propanol for CO₂ capture and metal-free catalysis in CO₂–epoxide cycloaddition reactions. The novel CAP-DAP material was characterized using various analytical techniques. It showed very good CO₂ adsorption capacity of 153 mg/g along with a high (CO₂/N₂) selectivity of 86 at 273 K/1 bar, in contrast to bare CAP, which exhibited moderate CO₂ adsorption of 136 mg/g with a CO₂/N₂ selectivity of 47. CAP-DAP also displayed high catalytic activity for CO₂–epoxide cycloaddition reactions under mild and solvent-free conditions. The synergistic effect between metal-free CAP-DAP and tetrabutylammonium bromide (<i>n</i>-Bu₄NBr) enabled a high epoxide conversion of 98% coupled with an excellent product selectivity of 99% at 60 °C, 1 bar CO₂, and a reaction time of 12 h. Faster reaction kinetics with reaction times <6 h was possible at 80 °C. The catalyst also showed excellent reusability and no leaching of active species was observed from the spent catalyst. Based on experimental results, a plausible reaction mechanism for CO₂–epoxide cycloaddition reaction over CAP-DAP catalyst has been proposed