Reaction Mechanism of H2-Assisted C3H6-SCR over Ag-CexZr Catalyst as Investigated by In situ FTIR

A series of silver-doped cerium zirconium oxide(Ag-CevZr)samples was synthesized successfully for selective catalytic reduction of nitric oxide(NO)with hydrogen and propene(H2/C3H6-SCR)under excess oxygen condition.The catalytic activity test proved that Ag-Ce0.4Zr exhibited the best C3H6-SCR activity.Hydrogen(H2)significantly enlianced NO conversion and widened the temperature window.Multi-technology characterizations were conducted to ascertain the properties of fabricated catalysts including X-ray diflraction(XRD),Fourier transform infrared spectrometry(FTIR),scanning electron microscopy(SEM)and H2 temperature programmed reduction(H2-TPR).In situ FTIR results demonstrated that various types of nitrates and chelating nitrite were generated on Ag-CexZr after introduction of NO.Besides,adding H2 could increase the concentration of bidentate nitrate and chelated bidentate nitrate dramatically,especially for Ce0.4Zr catalyst.Transient reaction between pre-adsorbing NO and C3H/C3H6+H2 illuminated that the most active intermediate was chelating nitrite,which was promoted significantly by H2 participation.Furthermore,adding H2 improved the formation of organo-nitro(R-N02),which was the key intennediate in C3H6-SCR.The reaction mechanism over Ag-CexZr catalysts was proposed at 200℃ as follows:nitric oxide(NO)+pr opene(C 3H6)+hy dr ogen(H2)+oxy gen(O2)→chelating nitrite (N O2-)+acry late-type species(CxHyOz)→organo-nitro(R-NO2)→isocyanate(-NCO)+cyanide(—CN)→nitrogen(N2).

Pyrolysis characteristics of Radix Rhizoma Rhei, Cortex Moudan Radicis, and Radix Sanguisorbae and correlations with the carbonizing process of Chinese herbs

AIM： The aim of the work is to study the pyrolysis characteristics of Radix Rhizoma Rhei, Cortex Moudan Radicis, and Radix Sanguisorbae in an inert atmosphere of argon （Ar）, and to investigate the mechanism of the carbonizing process of the three traditional Chinese herbs. METHODS： The pyrolysis characteristics of the crude materials and their extracts were studied by thermogravimetry-mass spectrometry （TG-MS） in a carrier gas of argon, coupled with Fourier transform infrared spectrometry （FTIR） and scanning electron microscopy （SEM） methods. Correlation of the pyrolysis behaviors with the carbonizing process by stir-frying of traditional Chinese medicines was made. RESULTS： Within the temperature range of 200-300 ℃, which is the testing range for the study of the carbonizing process of Chinese herbs, the temperatures indicated by the maximum weight loss rate peak of the above three extracts were taken as the upper-limit temperatures of the carbonizing process of the herbs, and which were 200, 240 and 247 ℃ for Radix Rhizoma Rhei, Cortex Moudan Radicis, and Radix Sanguisorbae, respectively. The ion monitoring signal peaks detected by the TG-MS method corresponded with reports that the level of chemical components of traditional Chinese medicinal materials would decrease after the carbonizing process. It was confirmed by Fourier transform infrared spectrometry （FTIR） and scanning electron microscopy （SEM） methods that better results of ＂medicinal property preservation＂ could be obtained by heating at 200 ℃ for Radix Rhizoma Rhei, at about 250 ℃ for Cortex Moudan Radicis, and Radix Sanguisorbae, as the relative intensity values of the common peaks were among the middle of their three carbonized samples by programmed heating. CONCLUSION： The upper-limit temperatures of the carbonizing process for Radix Rhizoma Rhei, Cortex Moudan Radicis and Radix Sanguisorbae were 200, 240 and 247 ℃ respectively. It is feasible to research the mechanism and technology of the carbonizing process of traditional Chinese medicinal materials using thermogravimetry, Fourier transform infrared spectrometry, and scanning electron microscopy methods.