X-ray Absorption Spectroscopy and Synchrotron X-ray Powder Diffraction Study of Pt-Ru, V2O5-TiO2, and Zeolite-Binder Interactions

• Main Authors: Chen, Nan Yu, 陳南宇
• Other Authors: Chang, Jen Ray
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/14958981193548362673

博士 === 國立中正大學 === 化學工程研究所 === 104 === The purpose of this research was to investigate the effect of bimetallic interaction to catalytic reaction. This study was divided into three parts. First, we discussed the metal-to-metal interaction. Pt-Ruco/C catalyst was prepared by co-impregnation and Ru-Ptse/C catalyst was prepared by successive impregnation, respectively. Those samples were characterized by XAS and TPR. When Pt(absorber)-Ru(backscatter) phase-and-amplitude correction was applied to Fourier-transformed EXAFS of Ru-Pt black at Pt edge, the characteristic peak of Pt-Ru interactions appears at 2.70 Å, whereas, when Pt-Pt correction is applied, the peak appeared at about 2.5 Å. The interactions also could semi-quantitatively be determined by the relative intensity between Pt-Ru and Pt-Pt characteristic peaks. This simple method in determining bimetallic interaction could be extended to characterize Pt-Pd/γ-Al2O3. However, for Pt-Re/γ-Al2O3, Pt-Re interactions cannot be determined by the method because of overlap of Pt-Pt and Pt-Re characteristic peaks due to similar phase functions. The second part was about the metal-support interaction for vanadia redox catalysts. To understand the role of TiO2, V2O5/SiO2, V2O5/TiO2, and V2O5/TiO2-SiO2 having different structures were prepared by incorporating vanadium oxytripropoxide on granular SiO2, TiO2 nano-particles, and TiO2-grafted-SiO2 pellets, respectively. In order to accelerate the catalyst deactivation, the catalysts were tested for oxidation of 1,2-dichlorobenzene with temperature elevated from 200 to 550oC. Using EXAFS and XRPD, the structural changes in the accelerated aging tests were characterized to assess the catalyst stability and the role of the grafted TiO2 in catalysis. The correlation of catalyst structures with catalytic reaction results indicated that: (1) the grafted TiO2 helps anchoring and dispersing vanadia in the catalyst preparation; (2) monomeric vanadia species with umbrella geometry, polymeric VO4, and TiVO4 coexisting with V2O5 clusters were formed on TiO2-SiO2 pellet, granular SiO2, and TiO2 nano-particles, respectively; (3) oxidative destruction of 1,2-dichlorobenzene induces the aggregation of vanadia species on the supports leading to a decrease of catalytic activity; (4) lower total oxidation selectivity for V2O5/TiO2 as opposed to the other two catalyst samples could be due to the presence of higher Brønsted-to-Lewis acid sites ratio; (5) a decrease of vanadium-atoms valence charge induced by TiO2-V2O5 interactions alleviates strong adsorption of oxygen-containing intermediates on vanadia sites, thereby increasing the reaction rate; and (6) hydration of vanadia in reaction could lead to aggregation of the vanadia species and catalyst deactivation. The last part was to discuss the interaction for support-to-binder. NaY-SiO2 extrudate was prepared by blending NaY powder with silica gel, and followed with kneading, extruding and calcination. The impact of silica binder on the structure and surface properties of NaY-SiO2 extrudate was investigated. Nitrogen adsorption/desorption isotherm suggests the formation of cylinderical meso-pores for NaY-SiO2. XRPD, TEM, and FT-IR suggest that in kneading, dealumination and cleavage of the intra-crystalline Si–O–Al bond via acid hydrolysis occur. This acid hydrolysis causes shrinkage of zeolite lattice along zeolite channel due to dislodgement of Al3+cations. The dealumination increases silica/alumina ratio of NaY concomitantly with the removal of Na+ leading to increase in the hydrophobicity of NaY, while reaction of silica binder with NaY debris and/or aluminum residue forms new Brønsted acid sites. Moreover, backfilling the vacancies created in the dealumination by mobile Si(OH)4 makes the zeolite more thermally stable, which lends the extrudate itself to industrial applications.