Recovery of NO: Energy-Efficient and Structure-Driven Clathrate-Based Greenhouse Gas Separation.

NO has 300 times more global warming potential than CO and is also one of the main stratospheric ozone-depleting substances emitted by human activities such as agriculture, industry, and the combustion of fossil fuels and solid waste. We present here an energy-efficient clathrate-based greenhouse gas-separation (CBGS) technology that can operate at room temperature for selectively recovering NO from gas mixtures. Clathrate formation between α-form/β-form hydroquinone (α-HQ/β-HQ) and gas mixtures reveals guest-specific and structure-driven selectivity, revealing the preferential capture of NO in β-HQ and the molecular sieving characteristics of α-HQ. With a maximum gas storage capacity and cage occupancy of 54.1 cm g and 0.86, respectively, HQ clathrate compounds including NO are stable at room temperature and atmospheric pressure and thus can be easily synthesized, treated, and recycled via commercial CBGS processes. High selectivity for NO recovery was observed during β-HQ clathrate formation from NO/N gas mixtures with NO concentrations exceeding 20%, whereas α-HQ traps only N molecules from gas mixtures. Full characterization using X-ray diffraction, scanning electron microscopy, Raman spectroscopy, solid-state nuclear magnetic resonance, and compositional analysis and the formation kinetics of HQ clathrates was conducted to verify the peculiar selectivity behavior and to design the conceptual CBGS process. These results provide a new playground on which to tailor host-guest materials and develop commercial processes for the recovery and/or sequestration of greenhouse gases.