Structure Sensitivities of SAPO Zeolites on Catalytic Oxidation of Nitric Oxide

摘要

NO_x emissions from increasing coal consumption, associated with respiratory diseases, ozone depletion, photochemical smog, acid rain, and ambient particulate matter, has triggered global interest in exploring new catalysts and technologies for NO_x abatement. Catalytic NO oxidation combined with subsequent liquid absorption is a possible alternative to current selective catalytic and non-catalytic reduction. Compared to existing abatement strategies, NO oxidation operates at a lower temperature (＜ 100 °C) and can potentially be used for simultaneous control of multiple pollutants. In this paper, we systematically investigate porous zeolites including SAPO-11 and SAPO-34 as NO oxidation catalysts, building upon previous work that shows activated carbon to be effective for this reaction. Our bench-scale reactor uses 2.4×10~4 mL·g~(-1)·h~(-1), 0.25 g of packed zeolite catalyst, 25 °C, 50 °C, and inlet gases of 380 ppm_v NO, 10 vol% O_2, and balance N_2. At 25 °C, higher conversion efficiency (39.78 ± 0.48%) was achieved on SAPO-34 than on SAPO-11 (7.85 ± 0.33%), and the corresponding conversion efficiency at 50°C for SAPO-34 is 16.2±0.7%, higher than 3.9±0.4%. Transient kinetic experiments combined with tests investigating the impacts of pre-sorbed NO_X species show that the NO oxidation mechanism over zeolite catalysts is consistent with the carbon-catalyzed process. Conversion efficiency of the catalyst is controlled by the catalyst's pore structure, including cavity size and channels. The pore width must be large enough to adsorb NO and formed intermediates, but narrow enough to provide the necessary energy benefits associated with increased adsorption in micropores.