Pillared Clays as Superior Catalysts for Selective Catalytic Reduction of Nitric Oxide


Book Description

In the last annual reports, we reported Cu-exchanged pillared clays as superior selective catalytic reduction (SCR) catalysts. During the past year we explored the possibilities with MCM-41, a new class of molecular sieve. In this report, Rh exchanged Al-MCM-41 is studied for the SCR of NO by C3H6 in the presence of excess oxygen. It shows a high activity in converting NO to N2 and N2O at low temperatures. In situ FT-IR studies indicate that Rh-NO species (1910-1898 cm−1) is formed on the Rh-Al-MCM-41 catalyst in flowing NO/He, NO+O2/He and NO+C3H6+O2/He at 100-350 C. This species is quite active in reacting with propylene and/or propylene adspecies (e.g., [pi]-C3H5, polyene, etc.) at 250 C in the presence/absence of oxygen, leading to the formation of the isocyanate species (Rh-NCO, at 2174 cm−1), CO and CO2. Rh-NCO is also detected under reaction conditions. A possible reaction pathway for reduction of NO by C3H6 is proposed. In the SCR reaction, Rh-NO and propylene adspecies react to generate the Rh-NCO species, then Rh-NCO reacts with O2, NO and NO2 to produce N2, N2O and CO2. Rh-NO+ and Rh-NCO species are two main intermediates for the SCR reaction on Rh-Al-MCM-41 catalyst.




Pillared Clays as Superior Catalysts for Selective Catalytic Reduction of Nitric Oxide. Second Semiannual Report, 1996


Book Description

During the first six months of the program, the work has progressed as planned. We have constructed a reactor system and assembled all laboratory essentials for conducting the three-year project. First, the catalytic activities of the Cu(2+) ion exchanged alumina-pillared clay for the selective catalytic reduction of NO by ethylene were measured. The temperature range was 250-500°C. The activities of this catalyst were substantially higher than the catalyst that has been extensively studied in the literature, Cu-ZSM-5. Fourier Transform Infrared Spectroscopy (FTIR) was used to study the acidity of the catalyst. The second part of the work was an in-depth FTIR study of the NO decomposition mechanism on the catalyst. This was planned as the first and the key step to obtain an understanding of the reaction mechanism. Key surface intermediates were identified from the FTIR spectra, and a redox type Eley-Rideal mechanism was proposed for the NO decomposition on this catalyst. This report will be divided into two parts. In Part One, we report results on the catalytic activities of the Cu-alumina-pillared clay and a direct comparison with other known catalysts. In Part two, we focus on the FTIR study and from the results, we propose a NO decomposition mechanism on this new catalyst. Plans for the next six months include tests of different pillared clays as well as the catalytic mechanism. The micro reactor will continue to be the key equipment for measuring the catalytic activities. FTIR will continue to be the major technique for identifying surface species and hence understanding the reaction mechanism.




Superior Catalysts for Selective Catalytic Reduction of Nitric Oxide. Final Technical Report, October 1, 1993--September 30, 1995


Book Description

The most advanced and proven technology for NO(subscript x) control for stationary sources is Selective Catalytic Reduction (SCR). In SCR, NO(subscript x) is reduced by NH3 to N2 and H2O. The commercial catalysts are based on V2O5/TiO2, and the vanadium-based catalysts are patented by the Japanese (Mitsubishi). However, there are three main advantages for the vanadium-based SCR catalyst: (a) a tendency to be poisoned in the flue gas; (b) oxidation of SO2 to SO3 by V2O5, this is a particularly severe problem due to the higher sulfur content of American coals compared with coals used in Japan (from Australia) and in Europe; (c) environmental problems involved in the disposal of the spent catalyst (due to the toxicity of vanadium). In order to overcome these problems, in addition to the undesirable dominance by the Japanese patent position, the authors have studied in this project a new type of catalyst for the SCR reaction; namely, pillared clays, which have adjustable, unique structures and acidity. Three types of catalysts were developed and tested for this reaction, i.e. Fe2O3-pillared clays, delaminated Fe2O3-pillared clays, and ion-exchanged pillared clays. The project was divided into sixteen tasks, and will be reported as such.










Superior Catalysts for Selective Catalytic Reduction of Nitric Oxide. Annual Technical Report, September 30, 1993--September 29, 1994


Book Description

A delaminated Fe2O3-pillared clay catalyst was prepared for the selective catalytic reduction (SCR) of NO by NH3 at above 300°C. The delaminated pillard clay was characterized by ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectroscopy) chemical analysis, XRD (X-ray diffraction) structure and line broadening analyses, micropore size probing, and Moessbauer analysis. These analyses showed that the catalyst contained fragmented Fe2O3-pillared clay forming {open_quotes}house-of-cards{close_quotes} structure with dispersed Fe2O3 particles approximately 170 Å in size. The SCR activity of the delaminated pillard clay was higher than the commercial-type V2O5 + WO3/TiO2 catalyst, and also higher than the undelaminated pillard clay and supported Fe2O3 catalysts, under conditions with SO2. Infrared measurements of adsorbed NH3 showed strong Bronsted acidity which was caused possibly by interactions between Fe2O3 and clay.




Superior Catalysts for Selective Catalytic Reduction of Nitric Oxide. Quarterly Technical Progress Report, 1 January 1994--31 March 1994


Book Description

During the past quarter, progress has been made in four tasks as summarized below: Task 1: A delaminated Fe2O3 pillared clay was synthesized and carefully characterized. The chemical composition was measured by ICP atomic emission spectrometry. The structural changes in the clay as well as the iron oxide particle sizes were characterized by X-ray diffraction techniques. Task 2: The Selective Catalytic Reduction (SCR, i.e., NO reduction with NH3) activities of the delaminated pillared clay were tested and compared with four other most active SCR catalysts: a commercial V2O5 + WO3/TiO2 catalyst, a Fe2O3-pillared clay, and two supported Fe2O3 catalysts (on Al2O3 and TiO2). The delaminated Fe2O3 pillared clay exhibited the highest SCR activities. Catalyst stability test showed that the delaminated sample was also stable. Task 3: To further increase the SCR activity of the delaminated pillared clay, Cr2O3 was doped as a promoter by incipient wetness. Task 4: Deactivation effects of SO2 and H2O on the SCR activities of the delaminated Fe2O3 pillared clay were studied, and compared with other SCR catalysts. The delaminated clay catalyst showed the least deactivation.




Superior Catalysts for Selective Catalytic Reduction of Nitric Oxide. Quarterly Technical Progress Report, July 1, 1995--September 30, 1995


Book Description

During the last quarter, we studied selective catalytic reduction (SCR) of NO with ethylene over Cu{sup 2+}-exchanged pillared clay and the important effect of O2 concentration. Also, the mechanism of the reaction was discussed. Details are presented in this report.




Superior Catalysts for Selective Catalytic Reduction of Nitric Oxide. Quarterly Technical Progress Report, January 1, 1995--March 31, 1995


Book Description

During this quarter, progress was made on the following tasks: TPD techniques were employed to study the reaction mechanism of the selective catalytic reduction of nitrogen oxide with ammonia over iron oxide pillared clay catalyst; and a sulfur dioxide resistant iron oxide/titanium oxide catalyst was developed.