The mechanism of gas-phase dehydration of cyclohexanol and the methylcyclohexanols catalysed by zirconium phosphate and zirconium phosphite

Costa, Magda; Hodson, Lisa F.; Johnstone, R. A. W.; Liu, Jun-Yao; Whittaker, D.

doi:10.1016/s1381-1169(98)00330-6

Cited by 20 publications

(4 citation statements)

References 16 publications

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“…In the literature, some metal carbonates, phosphates, and sulfates have been used as supports to load metals [2]. From the examples on the catalytic applications of metal phosphate-based catalysts cited in the Introduction section [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,…”

Section: Resultsmentioning

confidence: 99%

“…In a classic book written by Tanabe, Misono, Ono, and Hattori, metal phosphates are highlighted as a new family of solid acids showing some promising applications in heterogeneous catalysis [3]. Metal phosphates can be used as catalysts directly, for instance, in the partial oxidation of propane [4], oxidative dehydrogenation of isobutane to isobutene [5,6,7], oxidative dehydrogenation of ethylbenzene to styrene [8], dehydration of cyclohexanol and 1-methylcyclohexanol [9,10,11], retro-Prins reaction [12,13], terpene rearrangements [14], alkylation of anisole with alcohols [15], dehydrofluorination of CF 3 CH 3 into CF 2 CH 2 [16,17], hydrolysis of CCl 2 F 2 [18,19,20], decomposition of CF 4 [21,22], decomposition of CH 2 FCF 3 [23], decomposition of chlorobenzene [24], decomposition of SF 6 [25,26], and hydrolysis of NF 3 [27]. …”

Section: Introductionmentioning

confidence: 99%

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Metal Phosphate-Supported Pt Catalysts for CO Oxidation

et al. 2014

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Oxides (such as SiO2, TiO2, ZrO2, Al2O3, Fe2O3, CeO2) have often been used to prepare supported Pt catalysts for CO oxidation and other reactions, whereas metal phosphate-supported Pt catalysts for CO oxidation were rarely reported. Metal phosphates are a family of metal salts with high thermal stability and acid-base properties. Hydroxyapatite (Ca10(PO4)6(OH)2, denoted as Ca-P-O here) also has rich hydroxyls. Here we report a series of metal phosphate-supported Pt (Pt/M-P-O, M = Mg, Al, Ca, Fe, Co, Zn, La) catalysts for CO oxidation. Pt/Ca-P-O shows the highest activity. Relevant characterization was conducted using N2 adsorption-desorption, inductively coupled plasma (ICP) atomic emission spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), CO2 temperature-programmed desorption (CO2-TPD), X-ray photoelectron spectroscopy (XPS), and H2 temperature-programmed reduction (H2-TPR). This work furnishes a new catalyst system for CO oxidation and other possible reactions.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Metal Phosphate-Supported Pt Catalysts for CO Oxidation

et al. 2014

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“…There is only one previously reported attempt to elucidate the reaction mechanism of cyclohexanol dehydration. Whittaker and co-workers performed deuterium-labeling studies for the gas-phase dehydration of cyclohexanol over zirconium phosphate. , Dehydration experiments at 350 °C using 2,2‘,6,6‘-[ 2 H 4 ]cyclohexanol as the starting material generated cyclohexene with significant deuterium scrambling. The authors attributed this outcome to the reaction intermediate being a carbocation with highly mobile positive charge, in which case the dehydration mechanism would be E1.…”

Section: Reaction Mechanismmentioning

confidence: 99%

Kinetics and Mechanism of Cyclohexanol Dehydration in High-Temperature Water

Akiya

Savage

2001

Ind. Eng. Chem. Res.

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We examined cyclohexanol dehydration in pure water at temperatures of 250, 275, 300, 350, and 380 °C with water densities ranging from 0.08 to 0.81 g/cm 3 . Under these conditions, cyclohexanol dehydrates readily in the absence of added catalysts to form cyclohexene as the major product. The most abundant minor products are 1-and 3-methyl cyclopentenes. The reaction rate and product distribution at 380 °C show a remarkable sensitivity to the water density. At low densities, the reaction is slow, and cyclohexene is the only product. At high densities, the reaction is nearly complete, and methyl cyclopentenes appear along with cyclohexene. The experimental results implied a reaction mechanism that comprises two pathways: (1) reversible cyclohexanol dehydration to form cyclohexene through an E2 mechanism, and (2) subsequent cyclohexene protonation to form the cyclohexyl cation, which rapidly rearranges to form methyl cyclopentyl cations, which then lose a proton to form methyl cyclopentenes. A kinetics model based on the proposed mechanism was able to predict the striking effect of the water density on the product yields at 380 °C and, thereby, to demonstrate that the proposed mechanism captures the trends in the experimental data. An analysis of mechanistic issues regarding cyclohexanol dehydration in high-temperature water (HTW) revealed three roles for water. Water participates in elementary reaction steps as a reactant and as a product, water is the source of the acid catalyst (H 3 O + ), and water also drives the mechanism toward E2 by favoring, through solvation, the oxonium ion rather than the carbocation as the reaction intermediate. This study provides further evidence that acid-catalyzed reactions can be accomplished readily in HTW in the absence of added acid and that HTW has potential applications in environmentally benign industrial chemistry.

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“…Some of the results seem to be contradictory since the behaviour of the catalyst depended to a great deal on preparation details. Recently, the mechanism of cyclohexanol and methylcyclohexanol dehydration over amorphous zirconium phosphate has been elaborated [9][10][11]. It was shown that the dehydration of deuterium labelled cyclohexanol involves a carbocation with a long lifetime.…”

Section: Introductionmentioning

confidence: 99%