Showing papers by "Ralph T. Yang published in 1992"

Pillared clays as superior catalysts for selective catalytic reduction of nitric oxide with ammonia

Abstract: Five pillared clays (PILC) have been synthesized and tested for their activities in the selective catalytic reduction (SCR) of NO by NH 3 in the temperature range 250-450°C. They all showed considerable activities, in the decreasing order Cr 2 O 3 -PILC, Fe 2 O 3 -PILC, TiO 2 -PILC, ZrO 2 -PILC, and Al 2 O 3 -PILC. Cr 2 O 3 -PILC exhibited higher activities than a commercial (VTT) WO 3 -V 2 O 5 /TiO 2 catalyst, but its activity was severely decreased by SO 2 . Fe 2 O 3 -PILC showed activities comparable to that of V 2 O 5 /TiO 2 and was SO 2 resistant. Doping with cerium oxide significantly enhanced the activity; for Fe 2 O 3 -PILC, doping with 1.5-2% CeO 2 more than doubled its activity, and the resulting activity was significantly higher than that of the VTT commercial catalyst (both with and without SO 2 and H 2 O). The formed PILC catalyst will have a bimodal pore structure, with which a superior poison resistance has been demonstrated in SCR operation with a V 2 O 5 -based catalyst. Thus, the high activities and the potential poison resistance make pillared clays a promising new class of catalyst for SCR applications

Characterization by physisorption of a new class of microporous adsorbents : pillared clays

Abstract: In this study, adsorption data were used for characterizing the microporosity of five pillared clays pillared by oxides of Zr, Al, Cr, Fe, and Ti), a new class of adsorbents for gas separation. The results show that these pillared clays (PILCs) are highly microporous and possess pores of width no greater than 2 nm. A theoretical approach for calculating the micropore size distribution of pillared clays is outlined, and the calculated micropore size distributions are compared with the results obtained from probe molecule sorption data

Unique adsorption properties and potential energy profiles of microporous pillared clays

Abstract: The adsorption isotherms of O2, N2, CH4, CO2, SO2, and NO on five pillared clays (Zr, Al, Cr, Fe, and Ti-PILCs) are measured. The equilibrium selectivity of CH4/N2 on Al-PILC is greater than 5.0, which exceeds all known sorbents by a large margin. In addition, high SO2/CO2 equilibrium selectivities are observed on these pillared clays. The sorption characteristics of these pillared clays (PILCs) exhibit characteristic trends that are better understood with the aid of the potential energy profiles. A new semi-empirical approach is presented for the calculations of the potential energy profiles of PILCs. This approach requires the adsorption isotherms and an isotherm equation that accounts for the structural heterogeneity of the adsorbents. A comparison of the energy profiles obtained using the semi-empirical approach with the corresponding results obtained via the Kirkwood-Muller formalism, where only dispersion forces are taken into account, provides a measure of the importance of the electrostatic forces in the sorption characteristics of these PILCs. Sizable differences are observed for the potential energy profiles, indicating that the electrostatic forces are not negligible, and can significantly enhance the adsorption potential, resulting in large increases in the amounts adsorbed on these PILCs.

Strongly bonded oxygen in graphite : detection by high-temperature TPD and characterization

Abstract: Temperature-programmed desorption (TPD) of oxidized graphites shows significant amounts of CO desorption at temperatures about 1200 o C, in addition to that desorbed below 1200 o C (with a TPD peak at 980 o C). The low-temperature peak has been reported in the literature for a variety of carbons, both graphitic and nongraphitic

Lithium Type X Zeolite as a Superior Sorbent for Air Separation

Abstract: Li-X, Ba-X, and Li-A zeolites are prepared by ion exchange with the commercial Na-X (13X) and Na-A (4A) zeolites. At the ambient temperature (298 K), only Li-X exhibits a significant enhancement of...

Evolution of polypyrrole band structure: A scanning tunneling spectroscopy study

Abstract: Scanning tunneling spectroscopy (STS) has been used to determine the band structure of polypyrrole. The polypyrrole films were electropolymerized onto a highly oriented pyrolytic graphite surface using a rotating disk electrode. Differential conductance spectra measurements allowed us to follow the evolution of the band gap as a function of doping level. Before and after the STS measurements, the film structure was imaged by scanning tunneling microscopy. The STS results agree with data obtained by inverse photoemission spectroscopy

Process of removing sulfur oxides from gaseous mixtures

Abstract: A process is provided for removing sulfur oxides from gaseous mixtures such as flue gases or tail gases. The process involves contacting the gaseous mixture with a non-functionalized polymeric sorbent which is essentially hydrophobic, such as styrenic polymers. The process may utilize pressure swing adsorption techniques, and is capable of producing a desorption stream with an SO2 concentration suitable for immediate conversion to elemental sulfur by the Claus process.