Zinc promoted alumina catalysts for the fluorination of chlorofluorocarbons

Abstract

A range of catalysts consisting of zinc impregnated -Al2O3 has been examined for the fluorination of chlorofluorocarbons. Addition of zinc to -Al2O3 promotes steady state fluorination of CF2ClCFCl2 (CFC-113) to 1,1,1,2-tetrafluoro-2,2-dichloroethane (CFC-114a). Zinc promotion of fluorination activity was maximised at 6.5 wt%. Temperature programmed reaction (TPR) studies on pre-fluorided catalysts show that CCl4 is fluorinated by a sequential mechanism, with CCl3F a primary product and CCl2F2 a secondary product. The addition of zinc to -Al2O3 resulted in a low temperature feature in the TPR profile, and further analysis shows that there is a strong correlation between catalyst activity for CFC-113 fluorination and the concentration of fluorine associated with this low temperature feature. As the site population of the low temperature feature increases the apparent activation energy for the CFC-113 fluorination process decreases. Higher temperature HF pre-treatment resulted in a significant reduction of the population of this low temperature site compared to the standard conditions without pre-treatment, indicating that active fluorine consists of labile surface bonded H-F, rather than a metal fluoride such as AlF3 or ZnF2. Based on experiments investigating highly dispersed zinc on an activated carbon support, zinc adjacent to an Al 3+ ion is required for fluorination, since this allows adsorption of active HF in close proximity to a Lewis acid site, where the CFC can adsorb.

Synthesis and Characterization of High-Purity Mesoporous Alumina with Excellent Adsorption Capacity for Congo Red

“…As can be seen from the pore size distribution plots, the pore size of the material was mainly distributed in the range of 2–16 nm, while the cumulative pore volume curves and cumulative surface area curves of the material were in the range of 2–24.82 nm. Mesoporous materials are defined as pore sizes in the range of 2–50 nm porous material [ 59 ], therefore, the product was a porous, highly dispersed solid material with a large specific surface area and high activity, which confer good catalytic and adsorption properties [ 1 , 2 , 3 , 4 , 5 ].…”

“…High-purity alumina (HPA), one of the cutting-edge materials of the 21st century, is widely used in modern industrial products for its excellent physical and chemical properties, for instance, high strength wear and corrosion-resistant candle materials, special gas additives, advanced ceramic materials, catalysts and their carriers, biomedical, protective materials, single crystal materials, laser crystals and many other fields [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ]. Impurity elements are mostly present in alumina in the form of oxides, such as sodium oxide, iron oxide, silicon dioxide, etc., and diverse miscellaneous impurities have different effects on its performance, thus limiting the widespread use of alumina.…”

Síntesis y caracterización de NiMo5W/Al2O3 modificado con ZnO para la hidrodesnitrogenación de Indol

“…De ahí que, realizar la modificación del soporte busca disminuir las interacciones fase activa-soporte, y así obtener fases más dispersas y más reducibles que mejoren la actividad y la selectividad [10]. En este sentido, M. Borque y col. [11], estudiaron la HDS de gasoil y tiofeno, y la reacción simultánea de HDS y HDN de mezcla de gasoil-piridina, utilizando como soporte de catalizadores Co(Ni)Mo, alúmina dopada con TiO 2 , cuya actividad aumentó por su alta dispersión con el incrementó la cantidad de TiO 2 . La adición de zinc al soporte de Al 2 O 3 que realizaron M. Jones y col. produjo alta dispersión del zinc sobre la superficie (< 10 %), el cual se introdujo en las vacancias de la estructura de la alúmina [12].…”

Template-free method for the synthesis of high-pore-volume γ-Al2O3 nanofibers in a membrane dispersion microreactor

“…As one of the most important functional materials, alumina has attracted considerable attention in adsorption, catalysis, and catalyst support [1][2][3][4][5]. Mesoporous γ-alumina materials with different morphologies, including γ-alumina nanoparticles, nanorod-like material, nanosheets and fibrous alumina, have been synthesized for their specific applications in many areas [6][7][8][9].…”