Application of Laser Raman Spectroscopy in Catalysis Research

Raman spectroscopy using laser light source, because the laser has the characteristics of good monochromaticity, strong directionality, high brightness, coherence, etc., laser Raman spectroscopy and Fourier transform infrared spectroscopy have become a molecular structure study. The main means. The application of laser Raman spectroscopy in the field of catalysis has a history of decades, and has achieved rich results in the research of supported metal oxides, molecular sieves, in-situ reactions and adsorption.　　 Application of laser Raman spectroscopy in molecular sieve research: framework vibration of molecular sieve, characterization of heteroatom molecular sieve, synthesis of molecular sieve. Research on the adsorption of the catalyst surface: One of the main applications of Raman spectroscopy in the study of the adsorption behavior of the catalyst surface is to study the surface acidity of the catalyst using pyridine as an adsorption probe. Research on catalyst surface species: Raman spectroscopy has played an important role in the research of supported metal oxides. It can not only obtain structural information of surface species, but also correlate structure with reaction activity and selectivity. This is very important in the study of catalysis. However, due to the strong fluorescence interference of carriers, the conventional Raman spectroscopy studies of some oxides, especially low-load oxides, have encountered great difficulties. Research on the phase transition of the catalyst surface: research on the coordination structure and dispersion state of metal oxides, etc. Reflecting the structure of TO film, D means ~ layer of film, at ℃, only the Raman peak of anatase; 1 layer, 2 layer film is not good in crystallization, because of the diffusion of Fe, the burning time is short, the film is thin, etc.; 3, 4 layers The difference is not big, they all have the Raman peak of well-crystallized anatase; the position of the Raman peak will change with the particle size and pore size. The smaller the particle size will cause the peak position to shift, the peak asymmetrically widens, the peak intensity becomes weaker, and the pore size of the TiO2 film becomes smaller. This is reflected in the obvious change in the peak position at 142cm, from the position 142cm-1 to 145cm-1. It shows that the size of the particle size is 10nm. The experiment shows the UV Raman spectra of 2% molY at different calcination temperatures, and the laser source is 244nm. After calcining the sample at 500°C, five main peaks of 340, 374, 476, 613 and 640 cm-1 are given. From the relative intensities of the peaks at 340 and 374 cm-1 and the peaks at 476 and 630 cm, it can be seen that after calcination at 500 ℃, it mainly exists in the form of monoclinic phase. With the increase of the firing temperature, there is almost no change in the intensity, width and frequency of the spectral peaks. Only the monoclinic phase peak of zirconia was observed during the calcination process at 500 to 800°C.　The peak of the spectrum becomes wider, and two new peaks appear at 930 and 1070 cm. The 930cm peak is the Vu003dO symmetrical stretching vibration peak of polymerized vanadium oxide outside the framework, and the spectral peak is the Vu003dO symmetrical stretching vibration peak of the framework four-coordinate vanadium oxide. The author believes that the two peaks of 930 and 1070 cm-1 are not found in the visible Raman spectrum, because the excitation line of the 244vim wavelength excites the charge transition of the framework vanadium and non-framework vanadium species, so the resonance effect makes the intensity of these two peaks Enhancement, so that the UV Raman spectrum peaks of framework alum and non-framework alum species are obtained at the same time. The experimental results show that the UV Raman spectra of Siliealite1 and Fe-ZSM-5 are compared with the UV Raman spectra of Silicalite-1. The UV Raman spectra of Fe-ZSM-55 are at 516, 580, 1026, 1126 and 1185cm. Five new peaks appeared at -1. Since the ultraviolet excitation line is located in the charge transition region (250 rim) between the framework iron and oxygen, these peaks can be attributed to the resonance Raman peaks of the framework iron species. In addition, using UV Raman spectroscopy, the author also detected the presence of trace iron in sili-calite1 and ZSM-5 molecular sieves, which shows that UV resonance Raman spectroscopy is a sensitive and reliable means to characterize the framework heteroatoms in molecular sieves. (The above is edited by laser cutting machine, see http://www.gnlaser.com for details)