Textural properties, surface chemistry and cyclohexene conversion of AlPO4-Al2O3 catalysts (original) (raw)
Related papers
Skeletal isomerization of cyclohexene on Al2O3 and AlPO4–Al2O3 catalysts
Canadian Journal of Chemistry, 1984
Cyclohexene skeletal isomerization, in a microcatalytic pulse reactor, was investigated using Al2O3 and AlPO4–Al2O3 as catalysts. Apparent rate constants and apparent activation energies were calculated according to the kinetic model of Bassett–Habgood. Selectivity studies concluded that 1-MCP and 3-MCP were competitive products with a first-order kinetics. The rate constants as well as the selectivity at 1-MCP increase with an increase in the number and strength of stronger acid sites, measured by means of the irreversible adsorption of aniline in cyclohexane, at 298 K, using a spectrophotometric method. The parallel reaction pathway, proposed for AlPO4 catalysts, agrees with both the observed rates and selectivities using Al2O3 and AlPO4–Al2O3 catalysts.
Skeletal isomerization of cyclohexene on AlPO4 catalysts
Canadian Journal of Chemistry, 1983
The skeletal isomerization of cyclohexene, in a microcatalytic pulse reactor, was investigated by using aluminium orthophosphates (Al/P = 1) as catalysts. An attempt has been made to correlate the isomerization activity with the acid properties of the solids, measured by means of the irreversible adsorption of different organic bases in cyclohexane, at 298 K, using a spectrophotometric method.Apparent rate constants were calculated in terms of the kinetic model of Bassett and Habgood. Selectivity studies led to the conclusion that 1-MCP and 3-MCP were competitive products. Correlation between the kinetic selectivity factor, σ, and the number of strong acid sites has been sought.A possible parallel reaction pathway is proposed, which agrees with both the observed rates and selectivities.
Journal of Colloid and Interface Science, 1987
A series of A1PO4-TiO2 (APTi) catalysts containing different weight compositions is prepared by precipitation of AIPO4 on commercial TiO2 (pure anatase, Aldrich Chemie) using propylene oxide and characterized with respect to crystallinity, textural properties, and surface chemistry (acidity, basicity, one-electron donor, and one-electron acceptor properties). The acidity (amount and strength distribution) is found by means of the irreversible adsorption of organic bases by using a spectrophotometric method and is correlated with the reactivity for cyclohexene skeletal isomerization (CSI) in a pulse microreactor. The acidity is found to be slightly dependent on the calcination temperature but a decrease is observed when the A1PO4/TiO: ratio is lowered. Also, the presence of TiO2 causes a homogenization in the acid strength distribution of A1PO4 and in the inhibition of the A1PO4 crystallization by treatment temperatures of 1073 K. Thus, A1PO4-TiO2 catalysts are found to have moderately strong acidic properties even at calcination temperatures of 1073 K. Apparent rate constants, activation energies, and selectivities to 1-MCP are calculated in terms of Bassett-Habgood's kinetic model for first-order processes and compared to those obtained using pure A1PO4 catalysts. It is found that A1PO4-TiO2 catalysts are more active for the CSI process than A1PO4 catalysts, especially at calcination temperatures over 923 K, indicating increased strength of acidity. Selectivity studies indicate that 1-and 3-methylcyclopentenes (I-MCP and 3-MCP) are competitive, stable, primary reaction products coming from cyclohexene (CH).
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.
Adsorption Science & Technology, 2002
AlPO4 and Al2O3–AlPO4 mixed catalysts of different composition (Al/P > 1) were prepared and calcined in the temperature range 350–650°C. Such catalysts were characterized by DTA and X-ray diffraction methods, and by nitrogen adsorption studies at −196°C. Their acidity was determined using a calorimetric titration method while their catalytic activity towards the dehydration of isopropanol was determined using a pulse microcatalytic technique. The data obtained from XRD studies showed that pure AlPO4 when calcined at 650°C had a rather low crystallinity with its crystalline structure (which is of the α-cristobalite type) being characterized by poorly developed peaks. However, significant changes in the texture, surface acidity and catalytic activity were observed as a result of changing the chemical composition of the solid, with the surface area, total pore volume and surface acidity generally increasing with increasing alumina content. Sintering commenced above 550°C leading to ...
CHARACTERIZATION AND ACTIVITY OF CoMo/AlPO4 CATALYSTS
Phosphorus Research Bulletin, 1999
An aluminum phosphate AlPO4 has been synthesized so as to substitute for alumina as support of CoMo sulfide aimed to hydrotreatment Loading with CoMo oxides decreases the density of Bronsted sites, whereas that of Lewis sites increases in connection with the dehydration activity for 2-butanol. The pH of the impregnating solution of Mo ions affects the density of Lewis acid sites, and the proportion of monomeric and polymeric oxides. The best sulfided CoMo/AIPO4 catalyst for thiophene hydrodesulfurization is obtained for a pH of 6. The activity is compared to that of commercial CoMo/Al2O3 catalyst
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.