Effect of Chemical Composition on the Structure and Catalytic Behaviour of AlPO4 and Al2O3–AlPO4 Mixed Catalysts (original) (raw)
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Characterization and Catalytic Activity of Cr2O3–Al2O3/AlPO4 Catalysts
Adsorption Science & Technology, 2000
Five samples of Al 2 O 3 /AlPO 4 (Al/P = 1.75) and Cr 2 O 3-loaded Al 2 O 3 / AlPO 4 (wt% Cr 2 O 3 = 5-25) were prepared. The catalysts were obtained by thermal treatment of the corresponding samples in air at 823 K and were characterized using XRD and DTA techniques. The textural properties (surface area, total pore volume and mean pore radius) were determined from nitrogen adsorption data obtained at 77 K. The acidic properties of all the samples were measured calorimetrically. The catalytic conversion of isopropanol was studied using a microcatalytic pulse technique. No spinel structure was detected by both XRD and DTA techniques and only Cr 2 O 3 was detected for samples containing 15 wt% chromia. Loading Al 2 O 3 /AlPO 4 with Cr 2 O 3 led to significant changes in the texture, surface acidity and catalytic activity of the prepared catalysts. Al 2 O 3 /AlPO 4 catalysts exhibit no dehydrogenation activity, whereas loading with Cr 2 O 3 favoured the dehydrogenation of isopropanol to acetone.
Journal of Catalysis, 1988
In this paper, the influence of the starting aluminum salt (chloride, nitrate, or sulfate) and the pretreatment temperature (773-1273 K) on textural properties, crystal structure, and surface acidity of AlPOd (Al/P = 1) catalysts was studied in order to learn how preparation conditions affect catalyst activity in organocationic reactions. The catalysts were characterized using nitrogen adsorption, X-ray diffraction, infrared spectroscopy, and thermogravimetric analyses. The surface acid properties were determined using a dynamic method that consists of determining the AlPO.+'s catalytic activity in cyclohexene skeletal isomerization (CSI), a reaction that requires the presence of strong surface acid sites. Catalytic activity (as apparent rate constants), activation energies, and selectivities to I-methylcyclopentene (I-MCP) were calculated in terms of Bassett-Habgood's kinetic model for first-order processes in which the surface reaction is the controlling step and the partial pressure of the reactant is low. Significant differences in structure, texture, surface acidity, and catalytic activity in CSI were found, showing that the aluminum starting salt plays an important role in the final properties of AlPOd (Al/P molar ratio = 1) catalysts. Thus, aluminum nitrate yielded materials with higher surface area and low activity for CSI while aluminum sulfate resulted in higher surface acidity, and hence catalytic activity for CSI, although the sample is highly crystalline exhibiting low surface area. Aluminum chloride produces porous catalysts although they are less acidic.
Reaction Kinetics & Catalysis Letters, 1994
The AIPO 4 content in CrPO4-AIPO 4 (CrAIP-A) systems has a marked influence on thermal behavior, speeding up the transformation of amorphous CrPO 4 to crystalline ~-CrPO 4. Thus, XRD analysis showed that amorphous systems are formed at AIPO 4 loadings less than 50 wt.% and calcination temperatures below 1273 K. Moreover, on 50 wt.% AIPO 4 developed crystalline B-CrPO 4 in CrAIP-A systems for every calcination temperature. Besides, at 1273 K crystalline systems (8-CrPO 4 and tridimite-AiPO 4) are formed for every composition. Moreover, surface area at any calcination temperature increases with the rise in the AIPO 4 content. Also, a surface area decrease on increasing calcination temperature is shown. Furthermore, CrAIP-A catalysts thermally treated below 1273 K only exhibited hydrogen bonded hydroxy groups (90-H = 3450 cm-l).
Transition Metal Promoted Amorphous AlPO4Catalysts 1. Acid-Base and Textural Properties
Journal of colloid and interface science, 1996
AlPO 4 -Al 2 O 3 have been studied with different catalytic Transition metal promoted amorphous aluminium phosphate reactions . Although a number of researchers (M 0.05 Al 0.95 PO 4 ) samples were prepared (by precipitation and ( 18, 19 ) have studied the effect of transition metal substicalcination) and characterized by chemical analysis, TG, XRD, tution on the aluminium phosphate molecular sieves nitrogen adsorption-desorption isotherms, surface acidic-basic ( AlPO 0 n ) no detailed work has been carried out so far sites, and oxidizing-reducing sites. Chemical analysis shows that to find the effects of transition metal phosphates on the the P/(Al / M) ratio in all the cases is slightly less than 1. Nitrogen surface properties and catalytic activities of amorphous adsorption-desorption studies at liquid nitrogen temperature aluminium phosphate. The acid -base and structural propshows that all the samples have high specific surfaces and possess erties of first-row transition metal promoted amorphous both micro as well as meso pores in the range 2.6 to 3.8 nm. The acidic-basic and oxidizing-reducing sites on the surface of aluminium phosphate are reported in the present paper. amorphous aluminium phosphate increased with the addition of transition metals. Surface area, acid-base, and oxidizing-reduc-EXPERIMENTAL ing properties increased slightly with an increase in calcination temperature up to 600ЊC, then decreased to low values at 800ЊC. Key Words: aluminium phosphate; transition metal; surface area; acid-base and redox sites.
Textural properties, surface chemistry and cyclohexene conversion of AlPO4-Al2O3 catalysts
Materials Chemistry and Physics, 1989
The effects of surface dehydration on crystallinity, textural properties (surface area and pore volume) and surface acid-base properties of differently prepared AlP04-Al203 (75:25 wt%) systems have been studied. Physical characterization was carried out by N2 adsorption, TG and XRD ~asureaents and by infrared spectroscopy. The catalysts were characterized by surface acid-basic site concentrations using a spectrophotometric method and by their catalytic activities in cyclohexene skeletal isomerization (CSI) through the use of a microcatalytic pulse reactor. Al203 was found to increase both the surface area and pore volume of A1P04 through the inhibition of the A1P04 crystallization at 1073 K. Apparent rate constants and activation energies in CSI were obtained according to the kinetic model of Bassett-Habgood developed for first order processes. Selectivity studies lead to the conclusion that I-and 3-methylcyclopentenes are competitive stable primary reaction products coming from cyclohexene across a parallel reaction network. The addition of Al203 to AlP04 catalysts enhances considerably both the catalytic activity to 1-, 3-and 4-~thylcy~lopentenes (I-, 3-and 4-HCP) and the selectivity to l-MCP (u) in these systems for the CSI indicating an increased strong acidity.
Journal of Catalysis, 1988
Effects of thermal treatment (at 723 K), hydrothermal treatment [low-pressure steam vapor (34 Torr) at 723 and 923 K and water (at autogenous pressure) at 398 and 473 K], and acid-base treatment (at 473 K) on the structural stability and physical properties of porous carbon samples prepared from both natural and synthetic sources have been studied. These thermally, hydrothermally, and acid-base-treated carbons have been characterized using BET, thermogravimetric, and infrared techniques. Investigations of the treated carbon samples revealed that the thermal stability, pore structure, pore size distribution, and surface area are strongly affected by the thermal, hydrothermal, and acid-base treatments. The method of sample treatment influences the order of thermal stability and porosity and surface area (differences in surface area were attributed to differences in porosity, based on micropore and total pore volume). FTIR studies show that the carbon structures are significantly influenced by the hydrothermal and acid-base treatments. The surface and pore structure modifications of the microporous carbon have also been studied by controlled air decomposition and high temperature aliphatic and aromatic organic vapor deposition.
Materials Research, 2006
catalysts were investigated in the conversion of oleic acid to biofuels and biolubricant at 1 atm and at 623 K. The catalytic tests were performed in a fixed bed and continuous flow reactor, using an oleic acid-catalyst ratio of 4 and N 2 as the carrier gas. The reaction products were analyzed by gas chromatography and acidity measurements. N 2 adsorption-desorption, X ray diffraction, 31 P nuclear magnetic resonance and FT-IR spectroscopy were also employed to evaluate the textural, structural and acidic properties of the catalysts. The results showed that phosphoric acid impregnation improved the alumina decarboxylation activities, generating hydrocarbons in the range of gasoline, diesel oil and lubricant oil. The best catalytic performance was achieved with the highest surface area alumina impregnated with H 3 PO 4 , which was the solid that allied high total acidity with a large quantity of mesopores.
Anion treatment (F− or SO42−) of AlPO4-Al2O3 (25 wt.-% Al2O3) catalysts
Applied Catalysis A: General, 1993
Vapour-phase catalytic alkylation of phenol with methanol was carried out in a microcatalytic pulse reader on AlPO,-Al*OB catalysts, containing various amounts (l-3 wt.-%) of fluoride or sulfate anions. The methylation reaction gave a mixture of 0-and C-alkylated products (C-alkylation taking place preferentially at the or&-position). The influences of the methanol/phenol molar ratios (0.5-8), the reaction temperature (523-673 K) and both anion type and anion loading upon the conversion of phenol and the selectivities of the products were investigated. The increase in surface acidity by anion loading (especially in the case of fluoride ion) increases both the 0-alkylation selectivity (mainly to anisole) and dealkylation processes; so that a lower phenol conversion (smaller pseudokinetic constant) and higher anisole selectivity is found for anion-modified AlPOd-A1*03 catalysts related to unmodified ones. From the distribution of methylated products and their OPE curves, an outline of catalyzed alkylation was presented.