Preparation Of Aluminum Pillared Clays Containing Rare Earth With Large Pore And Supported Catalysts For VOCs Oxidation

Volatile organic compounds (VOCs) from industrial emissions have contributed significantly to air pollution. The control of their emissions has therefore become imperative. Since the environmental legislation in China and elsewhere is imposing stringent standards on VOC emissions, efficient technologies for the removal of VOCs must be developed. The deep catalytic oxidation of these pollutants to carbon dioxide and water has been identified as one of the most efficient ways to destroy VOCs at low concentrations and to meet the increasingly stringent environmental regulations. Supported precious metals such as Pt and Pd are well established as efficient catalysts for VOC elimination. However, for obvious reasons, cheaper catalytic materials, involving base metal oxides, are of ever increasing importance. In China, clay resources are rich and pillared interlayer clays (PILCs) are considered to be a new generation of materials with layered structure and a two-dimension porous structure. PILCs have increased surface area, pore volume, thermal stability, and (depending on the pillars) improved catalytic activity compared to the parent clays, making them suitable catalysts, ion exchangers, and adsorbents. PILCs are usually adopted as supports in order to maintain favorable dispersion of active metal to achieve valid utilization. It is well known that rare earth (REE) as a structural promoting component enhances the metal dispersion, participates in stabilization of the support against thermal sintering, and improves the catalytic oxidation.ability of the catalystsIn the present dissertation, a series of high surface area and large pore Al-PILC, REE/Al-PILC and AlREE-PILC were synthesized through cation-exchange, intercalation and hydrothermal treatment (Normal temperature and pressure; High temperature and pressure) preparation approaches. The catalytic performances for deep oxidation of low concentrations of VOCs (about 150 ppm) over the synthetic clay-based materials supported Pd and transition metals (M) were studied. And the influence of REE addition to the catalysts had also been investigated. The structure and surface properties of synthetic clay-based composite materials were characterized by X-ray powder diffraction (XRD), N2 adsorption/desorption, Atomic force microscopy (AFM), High resolution transmission electron microscopy (HRTEM), Energy dispersive X-ray spectroscopy (EDX), Fourier transformed infrared (FT-IR) spectroscopy techniques. Some specific conclusions are drawn from this work as follows:1. Al-PILC were prepared and used as supports of rare earths and palladium catalysts for deep oxidation of low concentration of benzene had been studied. The results showed that pillaring caused a strong increase in basal spacing, surface area, and pore volume. After impregnating REE on Al-PILC, a super structure was found, which may be due to the fact that Ce3+ migrate to hexagonal Si-O cavities and locations in the interlayer of clays, after calcination, the Ce cations are converted to CeO2, which resulted in collapse of some clay layers and formed a new structure, defined as "house of card". The super structure was in favor of the interaction of REE, Al-PILC and Pd, and enhanced the dispersion of Pd particles on clay surface, which improved the activity of Pd/Al-PILC catalysts for benzene oxidation.2. High surface area and large pore Al/REE pillared clays (AlREE-PILC) were synthesized and used as supports for Pd catalysts in deep oxidation of low concentration of benzene. The results showed that AlREE-PILC had larger basal spacings, more surface area and pore volume compared to those of Na-mmt and Al-PILC. Especially for AlCe-PILC, which were characterized by basal spacings of 1.79-2.83 nm and have high surface areas of 343.6～377.4 m2/g. The optimized preparation conditions had great effects on surface area, pore volume, mesopore and micropore amount of AlREE-PILC. Catalytic activity tests showed that high mesopore surface area, large pore structures of AlREE-PILC enhanced the dispersion of Pd particles and thus increased the active sites, which improved the activity of the Pd/AIREE-PILC catalysts for low concentration of benzene oxidation, especially for Pd/AlCe-PILC. Pd/AlCe-PILC(5;30) exhibited the highest catalytic activity and the temperature for complete benzene oxidation was about 250℃.3. Al-PILC were used to support transition metals (M=Cr, Mn, Fe, Co, Ni, Cu) for low concentration of benzene oxidation, and the effect of Ce addition to M/Al-PILC catalysts had been investigated. The results showed that introduction of Ce into M/Al-PILC also resulted in a super structure. Proper CeO2 content can enhance the oxidation ability of metal oxide and improve dispersion of transition metals, which improved the activity of the catalysts. Mn based catalysts were observed to be the most active among the transition metals. After optimizing the preparation conditions of MnCe/Al-PILC catalysts, it was found that MnCe(18:1)/ Al-PILC exhibited the highest activity the ignite temperature was 190℃and the temperature for the complete benzene conversion using this catalyst was about 280℃. The catalyst had a considerable activity compared to precious metal catalysts, exhibiting good application prospects.4. The adsorption-desorption-catalytic oxiation properties and rules of different pore structure of clays supported Pd or transition metal catalysts of low concentration of VOCs were investigated. The results showed that PILCs have a pronounced increase in adsorption amount and in desorption temperature due to their porosity and surface area increasing, which improves the activity of the catalysts for low concentration of VOCs, especially for VOCs with big sizes. The results had extremely significance on improving adsorption in low temperature, desorption in high temperature and oxidation performance of integrated "adsorption-catalysis".