Showing papers by "Ralph T. Yang published in 2012"

Activity, propene poisoning resistance and hydrothermal stability of copper exchanged chabazite-like zeolite catalysts for SCR of NO with ammonia in comparison to Cu/ZSM-5

Abstract: Copper, iron, and mixed copper/iron exchanged zeolites containing ZSM-5 and chabazite-like zeolites (SSZ-13, SAPO-18 and SAPO-34) were studied for selective catalytic reduction (SCR) of NO with NH3 with or without propene. Cu/ZSM-5, Cu/SSZ-13, Cu/SAPO-18 and Cu/SAPO-34 exhibited high NO conversions without propene. However, as compared to Cu/ZSM-5, NO conversions over Cu/SSZ-13, Cu/SAPO-18 and Cu/SAPO-34 were more stable with propene, due to coke formation over Cu/ZSM-5. The results of N2-adsorption/desorption and XPS showed that the surface area, Cu+/Cu2+ ratio and the surface amount of Cu content of Cu/ZSM-5 catalysts changed from 324 m2/g, 0.03 and 11.5 wt% for the fresh Cu/ZSM-5 catalyst to 68 m2/g, 0.34 and 5.3 wt% for the used sample. However, there were little changes between fresh and used Cu/SSZ-13, Cu/SAPO-18 and Cu/SAPO-34 catalysts. Moreover, Cu/ZSM-5 catalyst showed a larger decline in NO conversion with time on stream and a higher adsorption amount of propene compared to Cu/SSZ-13, Cu/SAPO-18 and Cu/SAPO-34 catalysts. The resistance to hydrocarbon poisoning depended on the pore geometry of the zeolites. During NH3-SCR, the presence of medium-pore sizes in Cu/ZSM-5 led to hydrocarbon deposition, which blocked the active sites and also decreased the active intermediates needed for NO conversion. Cu/SSZ-13, Cu/SAPO-18 and Cu/SAPO-34 catalysts, on the other hand, with small pores and cage diameters and with one-dimensional channel structures, showed higher hydrocarbon poison resistance. Moreover, these copper exchanged small-pore zeolites showed much higher hydrothermal stability than the medium-pore Cu/ZSM-5.

Significantly Increased CO2 Adsorption Performance of Nanostructured Templated Carbon by Tuning Surface Area and Nitrogen Doping

Abstract: Carbon dioxide adsorption properties of a series of templated carbon adsorbents with high Brunauer–Emmett–Teller surface areas (1361–3840 m2/g) and with/without nitrogen doping (6–7 wt % N) were systematically studied. Two linear relationships between CO2 adsorption capacities and surface areas of nitrogen-doped/undoped nanostructured templated carbons were first established. The doped nitrogen was present in the forms of pyridinic nitrogen, pyrrolic/pyridonic nitrogen, quaternary nitrogen, and an oxidized form of nitrogen. The interaction energies with CO2, as approximated by the isosteric heats of adsorption, were increased from 30 kJ/mol on the undoped carbon to 50 kJ/mol on the N-doped carbon as a result of these nitrogen sites. The increased interactions led to an enhancement in CO2 adsorption capacity by a factor of 2, while N2 uptake was not enhanced. The optimized N-doped templated carbon, N-TC-EMC, possessed remarkable CO2 capacity (4 mmol/g at 1 atm and 298 K) and selectivity (CO2/N2 at 1 atm = ...