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  • 1
    Electronic Resource
    Electronic Resource
    A1PO4-Al2O3 catalysts with low alumina content. III. Surface basicity of catalysts obtained in aqueous ammonia (1993)
    Springer
    Catalysis letters 19 (1993), S. 137-142 
    Details
    ISSN: 1572-879X
    Keywords: AlPO4 ; AlPO4-Al2O3 ; surface basicity ; Langmuir adsorption ; Knoevenagel condensation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The amount of basic sites of A1PO4-Al2O3 (APA1-A, 5–15 wt% Al2O3) catalysts at two basic strengths was measured by studying the liquid-phase adsorption of two acidic molecules (benzoic acid (BA, pK = 4.2) and phenol (PH, pKa = 9.9) from cyclohexane solutions, through the application of a spectrophotometric method. The data obtained follow the Langmuir adsorption isotherm and the monolayer coverage at equilibrium (at 298 K),X m, is assumed as the amount of basic sites corresponding to the specific pK of the acid used as titrant. The amount of basic sites of any AlPO4-Al2O3 catalyst is higher than that of AlPO4, but lower than that of Al2O3. Besides, an increase in the Al2O3 content from 10 wt% gradually increases the basicity of the APA1-A catalyst. Moreover, calcination at increasing temperatures does not practically affect the surface basicity of APAl-A-5 and APAl-A-10 catalysts. However, for AlPO4 content higher than 10 wt% we observe a decrease in surface basicity, this decrease depends on alumina content, i.e. it is higher as the amount of alumina increases. The basic sites of APAl-A systems catalyze the Knoevenagel condensation ofp-methoxybenzaldehyde and malononitrile at room temperature and in the absence of solvent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00771748
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  • 2
    Electronic Resource
    Electronic Resource
    Fluoride treatment of AlPO4-Al2O3 catalysts. II. Poisoning experiments by bases for cyclohexene conversion and cumene cracking (1994)
    Springer
    Catalysis letters 24 (1994), S. 293-301 
    Details
    ISSN: 1572-879X
    Keywords: AlPO4-Al2O3 ; fluoride ion loading ; surface acidity ; cyclohexene conversion ; cumene cracking ; poisoning by bases ; pyridine ; 2,6-dimethylpyridine ; hexamethyldisilazane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Brønsted acid sites on fluoride-modified AlPO4-Al2O3 (2.5 wt% F; APAl-P-2.5F) catalyst are poisoned by the presence of 2,6-dimethylpyridine (DMPY) and hexamethyldisilazane (HMDS), thus decreasing the catalytic activity for cyclohexene and cumene reaction processes, while the effect of pyridine (PY) was scarce. Besides, the drop in activity for cyclohexene conversion was accompanied by a change in reaction selectivity so that hydrogen transfer sites are much more sensitive to base poisoning (getting greater as the poisoning effect increased) than isomerization sites. Moreover, surface trimethylsilyl (TMS) complexes (formed by covalent reaction of HMDS with surface hydroxyls) decomposed and thus, the activity progressively increased at increasing time intervals, thus reaching greater values (at ca. 4 h) than the unpoisoned APAl-P-2.5F catalyst. So, DMPY was more suitable than PY and HMDS for the poisoning of Brønsted acid sites on APAl-P-F catalyst.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00811802
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  • 3
    Electronic Resource
    Electronic Resource
    Continuous flow toluene methylation over AlPO4 and AlPO4-Al2O3 catalysts (1994)
    Springer
    Catalysis letters 26 (1994), S. 159-167 
    Details
    ISSN: 1572-879X
    Keywords: aluminum orthophosphate (AlPO4) ; AlPO4-Al2O3 ; toluene methylation ; methanol ; activity ; selectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Toluene methylation with methanol over AlPO4 (AP) and AlPO4-Al2O3 (APAl) catalysts, obtained through different methods, was carried out in a continuous down-flow fixed bed reactor. The main products were xylenes (XYL), although trimethylbenzenes (TMB) were also found over APAl catalysts. The benzene and ethylbenzene selectivities increased slightly with time on stream at the expense of XYL and TMB selectivities. Isomer distribution was approximately 50, 24 and 26 mol% foro-, m- andp-XYL, and 72, 27 and 0 mol% for 1,2,3-, 1,2,4- and 1,3,5-TMB. The initial reaction rate constants were higher on APA1 catalysts and, furthermore, APAl catalysts exhibited similar catalytic activities, although those obtained in ethylene or propylene oxide are the most active ones. The same occurs on AP catalysts. Moreover, the changes in catalytic activity are similar to the changes in the acidic characteristics measured, in gas phase, versus pyridine. Furthermore, the activity decreased with time on stream due to coke deposition according to the expressionk = k0 exp(-βt). The rate of deactivation, evaluated from the deactivation coefficients (β), was greater for APAl than for AP catalysts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00824041
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  • 4
    Electronic Resource
    Electronic Resource
    Phenol methylation over CrPO4 and CrPO4−AlPO4 catalysts (1997)
    Springer
    Reaction kinetics and catalysis letters 62 (1997), S. 47-54 
    Details
    ISSN: 1588-2837
    Keywords: chromium orthophosphate (CrPO4) ; chromium aluminium orthophosphates (CrPO4-AIPO4) ; surface acidity, phenol/methanol and phenol/dimethyl carbonate alkylation ; activity ; selectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The vapor-phase catalytic alkylation of phenol with methanol and dimethyl carbonate on a series of differently prepared CrPO4 (Cr/P=1) and CrPO4-AlPO4 (CrAIP) catalysts, has been studied at different temperatures (473–673 K). The reaction is first order in phenol, giving a mixture of O- and C-alkylated products (C-alkylation taking place preferentially at theortho-position). Moreover, dimethyl carbonate is a better methylating agent than methanol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02475712
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  • 5
    Electronic Resource
    Electronic Resource
    AlPO4−Al2O3 catalysts with low alumina content, VII. Anisole conversion in the presence of methanol (1995)
    Springer
    Reaction kinetics and catalysis letters 56 (1995), S. 349-362 
    Details
    ISSN: 1588-2837
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The conversion of anisole in the presence of methanol (anisole/methanol molar ratio=4) over AlPO4−Al2O3 (5–15 wt.% Al2O3) catalysts gave a mixture of dealkylated and C-alkylated products (C-alkylation preferentially inortho-position) in which dealkylation to phenol always predominated. The catalytic activity, which increased with alumina content and decreased on increasing the calcination temperature from 773 to 1073 K, was fairly well related to the change in surface acidic characteristics. Furthermore, anisole conversion followed the requirements of the Bassett-Habgood kinetic treatment for first order processes, with a single common interaction mechanism and, consequently, a common transition state for all catalysts. Poisoning by pyridine and 2,6-dimethylpyridine confirmed that anisole conversion occurs on acid sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02076040
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  • 6
    Electronic Resource
    Electronic Resource
    Isomerization of 3,3-dimethyl-1-butene over aluminum and chromium orthophosphates (1998)
    Springer
    Reaction kinetics and catalysis letters 64 (1998), S. 41-48 
    Details
    ISSN: 1588-2837
    Keywords: AlPO4 ; CrPO4 ; CrPO4−AlPO4 ; surface acidity ; 3,3-dimethyl-1-butene isomerization ; poisoning by bases ; pyridine ; 2,6-dimethylpyridine ; hexamethyldisilazane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The skeletal isomerization of 3,3-dimethyl-1-butene over AlPO4 (Al/P=1), CrPO4 (Cr/P=1), and CrPO4−AlPO4 (CrAlP, 5–10 wt.% AlPO4) catalysts is a first order reaction. Catalytic performance is affected by the precipitation agent. CrPO4 catalysts obtained in propylene oxide-aqueous ammonia showed the highest activity. Moreover, the incorporation of AlPO4 to CrPO4 developed CrAlP catalysts that exhibited increased activity, irrespective of the precipitation method, as compared with both AlPO4 and CrPO4 catalysts. Besides, CrAlP catalysts prepared in propylene oxide-aqueous ammonia were the more active ones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02475368
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  • 7
    Electronic Resource
    Electronic Resource
    Catalytic performance of Fe-modified AlPO4 catalyst in cyclohexene skeletal isomerization (1994)
    Springer
    Reaction kinetics and catalysis letters 53 (1994), S. 13-23 
    Details
    ISSN: 1588-2837
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Iron-modified AlPO4 catalysts (0.5–5 wt.% Fe2O3) have been prepared by impregnation until incipient wetness with different iron(III) salts. The resulting solids, after characterization by surface area, XRD and DRIFT measurements, were checked for their surface acidity through their catalytic activity towards cyclohexene skeletal isomerization test reaction. It was found that iron(III) increases the catalytic performance of AlPO4 and besides, the iron(III) salt used strongly influences the activity. Thus, the catalysts prepared using complexed iron(III) salts as starting materials presented higher specific activity (and hence, acidity) than those prepared using iron(III) nitrate. Moreover, a maximum in activity was found for 2 wt.% Fe2O3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02070108
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  • 8
    Electronic Resource
    Electronic Resource
    Chromium-aluminium orthophosphates, II. Effect of AlPO4 loading on structure and texture of CrPO4−AlPO4 (20–50 wt.% AlPO4 catalysts obtained in aqueous ammonia (1994)
    Springer
    Reaction kinetics and catalysis letters 53 (1994), S. 45-53 
    Details
    ISSN: 1588-2837
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The AlPO4 content in CrPO4−AlPO4 (CrAlP-A) systems has a marked influence on thermal behavior, speeding up the transformation of amorphous CrPO4 to crystalline β-CrPO4. Thus, XRD analysis showed that amorphous systems are formed at AlPO4 loadings less than 50 wt.% and calcination temperatures below 1273 K. Moreover, on 50 wt.% AlPO4 developed crystalline β-CrPO4 in CrAlP-A systems for every calcination temperature. Besides, at 1273 K crystalline systems (β-CrPO4 and tridimite-AlPO4) are formed for every composition. Moreover, surface area at any calcination temperature increases with the rise in the AlPO4 content. Also, a surface area decrease on increasing calcination temperature is shown. Furthermore, CrAlP-A catalysts thermally treated below 1273 K only exhibited hydrogen bonded hydroxy groups (υO-H≃3450 cm-1).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02070112
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  • 9
    Electronic Resource
    Electronic Resource
    Chromium-aluminium orthophosphates, III. Acidity and catalytic performance in cyclohexene and cumene conversions on CrPO4−AlPO4 (20–50 wt.% AlPO4) catalysts obtained in aqueous ammonia (1994)
    Springer
    Reaction kinetics and catalysis letters 53 (1994), S. 55-63 
    Details
    ISSN: 1588-2837
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The modification of CrPO4-A catalyst with AlPO4 leads to CrPO4−AlPO4 (CrAlP-A) catalysts exhibiting not only an increased total acidity but also an increased number of strongest Lewis acid sites as compared to CrPO4 and AlPO4 catalysts. Besides, surface acidity is slightly influenced by AlPO4 loading (5–50 wt.%). This increased surface Lewis acidity is responsible for the improved catalytic activity in cyclohexene skeletal isomerization and cumene dehydrogenation processes. Moreover, the catalytic activity results can be well interpreted through differences in the number and strength of acid sites, measured gas-chromatographically, in terms of pyridine and 2,6-dimethylpyridine chemisorbed at different temperatures (573–673 K).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02070113
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  • 10
    Electronic Resource
    Electronic Resource
    Conversion of anisole in the presence of methanol over AlPO4−Al2O3 catalysts modified with fluoride and sulfate anions (1995)
    Springer
    Reaction kinetics and catalysis letters 54 (1995), S. 99-106 
    Details
    ISSN: 1588-2837
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The gas-phase microcatalytic conversion of anisole in the presence of methanol (methanol/anisole molar ratio=4) was studied at temperatures ranging from 523 to 673 K over anion treated (1–3 wt.% F or SO 4 2− ) AlPO4−Al2O3 (25 wt.% Al2O3) catalysts. Anisole conversion gave a mixture of dealkylated and C-alkylated products (C-alkylation preferentially in ortho-position) where dealkylation always predominates. The influences of the reaction temperature and both anion type and anion loading upon the conversion of anisole and the selectivities of the products were investigated. The higher increase in surface acidity by fluoride loading increases both the C-alkylation selectivity (mainly to 2-methylanisole) and dealkylation to phenol; so that a lower anisole conversion (smaller pseudokinetic constant) and higher methylanisoles selectivity is found for APAI-P-F catalysts related to unmodified one.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02071186
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