Chromia Alumina Research Articles

Aromatization of isophorone to 3,5-xylenol

Aromatization of isophorone to 3,5-xylenol was studied in a continuous-flow fixed-bed reactor at temperatures of 450–580°C and space velocities of 0.5–4.0 h −1 at atmospheric pressure using γ-alumina and magnesia (prepared in the laboratory) and commercially available chromia—alumina as catalysts. With γ-alumina, decomposition of isophorone was the predominant reaction, resulting in low conversions to 3,5-xylenol. With magnesia and commercial chromia—alumina catalysts, the reaction path was found to be preferably the transformation of isophorone to 3,5-xylenol, conversion of isophorone to 3,5-xylenol increasing in the order γ-Al 2O 3<MgO<Cr 2O 3−Al 2O 3. Higher conversions of isophorone mainly to 3,5-xylenol were obtained with Cr 2O 3−Al 2O 3 than with the other two catalysts. Selectivity for the formation of 3,5-xylenol to the extent of about 90% could be obtained with chromia—alumina catalyst.

Catalytic hydrodealkylation of tar acids

The catalytic vapour phase hydrodealkylation of LT tar acid fractions to low boiling phenols was studied in a flow system in the temperature range 480–650°C, and over a wide range of space velocities on a chromia—alumina catalyst at atmospheric pressure. The feed, as well as the products, was analysed by gas chromatography. Optimum conditions for maximum yield of lower phenols were established. In the hydrodealkylation of tar acid fractions (i) b 170–210°C, (ii) b 210–230°C and (iii) b 230–270°C, the contents of lower phenols in the liquid products were found to be respectively, 98.6% (55.2 % phenol + 43.4% cresols), 85.5.% (27.4% phenol + 58.1% cresols) and 79.9% (26.8% phenol + 53.1% cresols) at 600°C. The catalyst was found to be highly specific in eliminating the dehydroxylation of phenolic substrates. The physico-chemical properties of the catalyst were determined. Based on an examination of the nature of the catalyst and the product pattern, a tentative mechanism for the reaction has been postulated. The results are interpreted as being due to the formation of chemisorbed phenoxy radicals and their subsequent reaction at the surface of the catalyst.

Active phases in chromia–alumina dehydrogenation catalysts. Electron spin resonance and kinetic studies

The rate of propane dehydrogenation on chromia–alumina has been measured in a flow system over the temperature range 800–891 K. Results show that the reaction rate dependence was of a fractional order (0.66) with respect to propane partial pressure, and an apparent activation energy of 138.8 kJ mol–1 was obtained. The effect of various pretreatments has been found to influence strongly both the e.s.r. spectra of the chromia phases and the activation energy of the reaction.

Hydrogenation of ethylene over chromia–alumina catalysts. Electron spin resonance and kinetic studies

The hydrogenation of ethylene over chromia–alumina catalysts containing known amounts of Cr2+ and Cr3+ has been investigated at temperatures between – 78 and 200 °C. The activity of the catalyst depends strongly on the presence of Cr3+(determined by e.s.r.), in as much as increasing Cr3+ concentration is accompanied by a considerable increase in the rate of hydrogenation. Preliminary kinetic studies show that the reaction rate is zeroth order in hydrogen at –78 °C and first order at higher temperatures (> 0 °C). The e.s.r. signal ascribed to Cr3+(g= 1.986) undergoes some changes under the reaction conditions when exposed to a 1 : 1 mixture of hydrogen and ethylene at 100 °C.

Surface composition and catalytic activity of chromia–alumina catalysts

The surface composition of chromia–alumina catalysts has been investigated. Electron spin resonance was used to follow changes in the signal ascribed to Cr3+ ions (at g= 1.986) after reduction in dry hydrogen (Cr2+ produced) and in hydrogen + water-vapour mixture at 500°C (only Cr3+ produced). The extent of reduction to Cr2+ depends on the concentrations of chromia present on the surface. Preliminary kinetic studies show that the rate of ethane dehydrogenation is higher on Cr2+ than on Cr3+ sites. Evidence supporting the presence of Cr2+ ions on the surface has also been provided.

Dehydrogenation of Δ3-carene over chromia and chromia–alumina catalysts

3-Carene is dehydrogenated over oxidized and reduced chromia and chromia–alumina catalysts at 340 to 500 °C, without and with pyridine. Dehydrogenation is found to be more effective over reduced than oxidized catalysts; in either state, however, chromia–alumina is more active than chromia. Pyridine brings down the dehydrogenation ability of chromia and chromia–alumina in both reduced and oxidized states, more markedly in the reduced state. The ratio of p-cymene to m-cymene at 360 to 425 °C is higher over chromia than over chromia–alumina. Increase of temperature from 360 °C to higher values decreases the ratio of cymenes over chromia but does not affect the ratio over chromia–alumina. Pyridine has no effect on the ratio of cymenes over chromia; over chromia–alumina, neither, pyridine nor the pretreatment of the catalyst with oxygen or hydrogen has any effect on the ratio.

Vapour phase catalytic transformations of terpene hydrocarbons in the C10H16 series. IV. Effect of nitrogen, hydrogen, and pyridine on the dehydrogenation of Δ3-carene over chromia and chromia-alumina catalysts

The influences of nitrogen, hydrogen, and pyridine on the conversion of 3-carene into various products over chromia catalyst at 450 °C and over chromia–alumina at 400 °C have been investigated. Nitrogen acts as a diluent over these catalysts; hydrogen at low partial pressures enhances the formation of cymenes over chromia, but suppresses its formation over chromia–alumina. Increase of the partial pressure of hydrogen increases the proportion of men thanes over chromia–alumina, but decreases it over chromia catalyst. Pyridine suppresses the over-all conversion of 3-carene and the formation of cymenes over chromia and chromia–alumina; however, it increases the formation of menthadienes over chromia–alumina. These observations are explained in terms of the acidity of chromia and chromia–alumina, the diluting effects of nitrogen, hydrogen, and pyridine, and their ability to adsorb and desorb over the catalyst surfaces.

Effect of ethylene and hydrogen adsorption on the e.s.r. spectra of chromia–alumina catalysts

The surface chemistry of Cr2+ and Cr3+ in chromia–alumina catalyst is investigated. Electron spin resonance studies revealed considerable changes in the behaviour of the signals ascribed to Cr3+(at g= 1.986) when exposed to H2, C2H4 and water vapour at 373 K. This work, when combined with the results from adsorption studies, allows some speculation upon the mode of adsorption of the gaseous species on the chromium ions.

Vapour phase catalytic transformations of terpene hydrocarbons in the C10H16 series. III. Dehydrogenation of Δ3-carene over modified chromia and chromia–alumina catalysts

The vapour phase dehydrogenation of 3-carene has been studied over chromia, chromia–alumina, chromia doped with potassium, and chromia–alumina doped with potassium and fluoride ions. Addition of potassium to chromia and chromia–alumina up to 1% by weight does not significantly affect the overall conversion of 3-carene whereas it increases its dehydrogenation to p- and m-cymenes. Potassium ions above 1% lower both the total conversion and dehydrogenation of 3-carene to cymenes. The ratio of p- to m-cymene over chromia–alumina is enhanced by added potassium ions up to 2%, but over chromia it remains unaffected. Addition of potassium to chromia decreases the formation of menthanes and menthadienes but its addition to chromia–alumina reduces the formation of menthanes and increases that of menthadienes. Impregnation of chromia–alumina with hydrofluoric acid suppresses the formation of menthadienes and increases that of menthanes. All these are explained in terms of the effect of added potassium and fluoride ions on the acidity of the catalysts.

X-Ray Photoelectron Spectroscopic Studies of Catalysts—Chromia–Alumina Catalysts—

Abstract The XPS studies of chromia–alumina catalysts were carried out to elucidate the surface of these catalysts. Photoreduction was found to occur during the XPS measurements. Therefore, all spectra were measured rapidly to prevent any photoreduction. It was found that the information about the spin-orbit splitting of the Cr2P level is very useful for determining the valence state of chromium. The surface state of chromium in chromia–alumina catalysts calcined at 500 °C for 5 h is predominantly Cr6+ at low chromia concentration catalysts. However, the Cr3+ phase appears in catalysts of higher chromium content, and the surface concentration of Cr3+ increases with increasing content of supported chromia. The XPS spectra due to Cr5+ were observed after mild reduction of the catalysts. Moreover, it was found that almost all surface chromium is present as Cr5+ at low chromia content catalysts after mild reductions. Qualitatively, the results obtained by the XPS technique, which gives information about the surface of catalysts, agree well with the results obtained by ESR and other techniques, which gives information about the bulk of catalysts, especially low chromium concentration catalysts. These findings indicate a high dispersion of chromium on γ-Al2O3 for low chromium content catalysts.

Vapor Phase Catalytic Transformations of Terpene Hydrocarbons in the C10H16 Series. II. Aromatization of α-Pinene over Chromia–Alumina

The aromatization of α-pinene in the vapor phase over chromia gel and chromia–alumina catalysts prepared from aluminas of different acidity has been studied. The acidity of alumina support has a remarkable influence on the composition of the aromatics resulting from the dehydrogenation of α-pinene. Over weakly acidic chromia–alumina doped with 1% sodium catalyst, α-pinene is aromatized to p-cymene, 1,2,4- and 1,2,3-trimethylbenzenes with traces of toluene and xylenes, whereas over the strongly acidic chromia – pure alumina and chromia–alumina containing 5% HF catalysts it gives considerable amount of m-cymene, toluene, and tetramethylbenzenes. A satisfactory mechanism to explain the formation of these compounds is offered.

Isomerization of butene over a chromia–alumina catalyst

Isomerization runs were performed in a micro-reactor at 325 °C over a range of butene partial pressure of 84 to 763 mm Hg and at a total pressure of approximately 1 atm. The isomerization rate of 1-butene passed through a maximum with increasing 1-butene partial pressure; the isomerization rate of cis- and trans-2-butene increased asymptotically with increasing cis- and trans-2-butene partial pressures respectively. Stereoselectivity was observed in the isomerization of each butene, and was found to be independent of pressure. Catalyst deactivation resulted in loss in stereoselectivity. Results suggest that surface reactions control isomerization and proceed simultaneously on different active sites.

Alumina: Catalyst and Support. XXIV.1 Discussion of the Mechanism of the Aromatization of Alkanes in the Presence of Chromia—Alumina Catalysts2,3

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAlumina: Catalyst and Support. XXIV.1 Discussion of the Mechanism of the Aromatization of Alkanes in the Presence of Chromia—Alumina Catalysts2,3Herman Pines and Charles T. GoetschelCite this: J. Org. Chem. 1965, 30, 10, 3530–3536Publication Date (Print):October 1, 1965Publication History Published online1 May 2002Published inissue 1 October 1965https://doi.org/10.1021/jo01021a058RIGHTS & PERMISSIONSArticle Views137Altmetric-Citations24LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (948 KB) Get e-Alerts Get e-Alerts

Alumina: Catalyst and Support. XXVI.1 Aromatization and Dehydroisomerization of Dimethylhexanes over Chromia—Alumina Catalyst. Contribution to the Mechanism of Aromatization2

Alumina: Catalyst and Support. XXVI.¹ Aromatization and Dehydroisomerization of Dimethylhexanes over Chromia—Alumina Catalyst. Contribution to the Mechanism of Aromatization²

Alumina: Catalyst and Support. XXV.1 Aromatization of 2-Methylhexane-6-C14, 3-Methylhexane-5-C14, and 3-Methyl-C14-hexane over Chromia—Alumina Catalyst. Contribution to the Mechanism of Aromatization2,3

Alumina: Catalyst and Support. XXV.¹ Aromatization of 2-Methylhexane-6-C¹⁴, 3-Methylhexane-5-C¹⁴, and 3-Methyl-C¹⁴-hexane over Chromia—Alumina Catalyst. Contribution to the Mechanism of Aromatization^2,3

Alumina: Catalyst and Support. XXVII.1 Aromatization of Methylcycloheptane and Methyl-C14-cycloheptane over Chromia—Alumina Catalyst. Contribution to the Mechanism of Aromatization2

Alumina: Catalyst and Support. XXVII.¹ Aromatization of Methylcycloheptane and Methyl-C¹⁴-cycloheptane over Chromia—Alumina Catalyst. Contribution to the Mechanism of Aromatization²

Indenols in coal tars : The first preparation of indenol

Recent work has disclosed that indenols are present in coal tars, but, until the present, no indenol has been isolated or synthesized. The first members of this class of reactive compounds have now been synthesized by catalytic dehydrogenation of indanols at 650° over chromia alumina with nitrogen gas as carrier. The indenols have been isoalted as white, crystalline, rather stable, solids. Dehydrogenation of 4-indanol yields 4- and 7-indenol; 5- and 6-indenols are obtained similarly fro 5-indanol. Separation of the indenols from starting indanol in each case was effected by ligand exchange chromatography. Each pair of indenols was then separated by gas chromatography. The 4- and 7-indenols prepared in this way were characterized by UV, IR and NMR spectra.

Optical Measurement of the Specific Chromia Area of Chromia—Alumina Catalysts

The optical reflectances of chromia—alumina catalysts in the visible and ultraviolet regions have been determined and, at the same time, the specific chromia surface areas measured by oxygen chemisorption. A relationship was found between the intensities of the charge-transfer bands of Cr6+ and the extent of chromia area, which permits one to determine the chromia area of a chromia—alumina catalyst from the optical reflectance spectra.

Electron Spin Resonance Study of the Antiferromagnetism of Chromia Alumina

Chromia alumina mixtures calcined between 500° and 1400°C were studied by electron spin resonance (ESR) in the temperature range from 125° to 550°K. The low-chromia content chromic ions are paramagnetic while at high-chromia contents the ESR spectra exhibit antiferromagnetic behavior. For Cr/Al ratios greater than ⅔ the 1400°C calcination samples produce sharp Néel points which increase with chromia content, while the samples with Cr/Al ratios less than ½ show broad Néel points which become less well resolved with decreasing chromia content. The spectra of high Cr/Al ratio samples calcined at 900°C and below are superpositions of a βw phase resonance which appears paramagnetic and a βn phase resonance which has a fairly sharp Néel point several degrees below the bulk chromia value, and the latter is attributed to clumps of chromia in the sample.

Alumina. Catalyst and Support. XXI.1 Aromatization of 2,4-Dimethyl-3-methyl-C14-pentane over Chromia—Alumina Catalyst. Contribution to the Mechanism of Aromatization2

Alumina. Catalyst and Support. XXI.¹ Aromatization of 2,4-Dimethyl-3-methyl-C¹⁴-pentane over Chromia—Alumina Catalyst. Contribution to the Mechanism of Aromatization²