Mechanism of dehydrogenation of secondary alcohols on chromia

Nondek, L.; Sedláček, Jiří

doi:10.1016/0021-9517(75)90223-7

Cited by 69 publications

(12 citation statements)

References 8 publications

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“…The spectroscopic results also showed that (presumably different) surface alkoxides are involved in the dehydration reaction according, on the dehydroxylated surfaces, to the modified Ipatieff mechanism involving (6) and (1 3). On the hydroxylated Ti0,(300) an Ipatieff mechanism involving reaction (5) instead of (6), or other mechanisms involving adsorbed alcohol as an intermediate, may also contribute to the catalytic process.…”

Section: Discussionmentioning

confidence: 99%

“…6(b)] and not from adsorbed alcohol. As water molecules are not observed until 300 OC, when the dehydration reaction has taken place, the 2-propoxide groups are probably produced by reaction (6). This reaction requires the generation of new OH-(s) groups and these are probably represented by a very broad and weak absorption band between ca.…”

Section: -Propoxide and Adsorbed Propan-2-01 As Surface Speciesmentioning

confidence: 99%

“…36 Considering first the dehydroxylated Ti02(800) surface, the spectroscopic evidence suggests that the 2-propoxide species are reactive intermediates, because these disappear from the surface as the dehydrogenation reaction commences, i.e. that the first step in the reaction is that described in eqn (6). There is indeed generally agreement that the acetone is derived from an alkoxide surface species.'.…”

Section: The Dehydrogenation Reactionmentioning

confidence: 99%

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Infrared spectroscopic studies of the reactions of alcohols over group IVB metal oxide catalysts. Part 1.—Propan-2-ol over TiO2, ZrO2 and HfO2

Hussein¹,

Sheppard²,

Zaki³

et al. 1989

J. Chem. Soc., Faraday Trans. 1

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Infrared spectroscopy has been used to analyse the gas-phase reaction products and the related adsorbed species obtained between room temperature and 400 "C from the dehydrogenation/dehydration reactions of propan-2-01 over a series of differently calcined catalysts of TiO,, ZrO, and HfO,. The ZrO, and HfO, results were independent of the calcination pretreatment, and the surfaces of these oxides, like that from a TiO, sample calcined at 800 "C, were dehydroxylated. Different results were obtained from a TiO, sample calcined at 300 "C which had a hydroxylated surface. The acidic sites and reactivities of the surfaces of Ti0,(300 "C) and Ti0,(800 "C) were explored by pyridine adsorption and infrared spectroscopy. Only Lewis-acid sites were detected by pyridine.On raising the reaction temperature, in all cases the dehydrogenation reaction to give acetone occurred either before or simultaneously to the onset of the dehydration reaction to give propene. Acetone production was most pronounced over ZrO, and HfO, but also occurred more with Ti0,(800 "C) than with Ti0,(300 "C). The dehydrogenation reaction was largely quenched by pre-adsorbed pyridine on both TiO, samples. The TiO, (300 "C) catalyst showed the presence of adsorbed propan-2-01 and 2-propoxide groups at room temperature. The dehydroxylated ZrO,, HfO, and Ti0,(800 "C) samples only showed appreciable amounts of 2-propoxide groups. In each case the 2-propoxide ions occurred in two different forms, presumably formed by adsorption on different types of sites.Both the acetone and propene products appeared as absorptions from 2propoxide surface species decreased in intensity, so the latter are clearly reactive species. Gas-phase acetone production was followed by the chemisorption of acetone at a higher temperature. This subsequently decomposed to give surface acetate species, and finally at 400 "C to give CO, and methane in the gas phase. Propene did not give rise to adsorbed species, or to further products in the gas phase.At the higher temperatures, above 300"C, the reaction was always selective in favour of the dehydration reaction. However, each of the dehydroxylated catalysts showed some selectivity in favour of the dehydrogenation reaction over the earliest temperature range for alcohol decomposition, between 200 and 250 "C.A discussion is given of possible mechanistic pathways for the production of surface 2-propoxide species and the two types of products, based on the infrared-supported assumption that the different adsorbed forms of 2propoxide [and possibly adsorbed propan-2-01 on Ti0,(300 "C)] are reactive intermediates.t On leave from Minia University.

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Section: Discussionmentioning

confidence: 99%

Section: -Propoxide and Adsorbed Propan-2-01 As Surface Speciesmentioning

confidence: 99%

Section: The Dehydrogenation Reactionmentioning

confidence: 99%

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Infrared spectroscopic studies of the reactions of alcohols over group IVB metal oxide catalysts. Part 1.—Propan-2-ol over TiO2, ZrO2 and HfO2

Hussein¹,

Sheppard²,

Zaki³

et al. 1989

J. Chem. Soc., Faraday Trans. 1

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“…Apparently, the activity of the materials is related to the presence of soluble and grafted chromates [27]. On the other hand, the reduction of these materials (M5CrSBA-15 and M10CrSBA15) does not change the initial conversion, but it inhibits deactivation [46]. The xCrSBA-15 materials present a greater deactivation, thus a greater number of acidic species (Cr 6+ ) or soluble chromates that dehydrate form Cr 2 O 3 determined by UV-vis (Figure 7), and they are also more susceptible to carbon poisoning or coke formation [47] Regarding the selectivity of the materials (Figure 6), the xCrSBA-15 materials increase their selectivity to propene in relation to time (Figure 6a) and the reduced MxCrSBA-15 materials decrease their selectivity after a few minutes (Figure 6b).…”

Section: Conversion Of 2-propanol On Xcrsba-15 Andmentioning

confidence: 99%

“…Similarly, the bands at 571 and 631 cm -1 decrease in intensity after the 2-propanol reaction. The change in these bands and the appearance of a small band at 1380 cm -1 may be attributed to the formation of C-H bonds that inhibit the activity of the materials [22,46].…”

Section: Ftir Spectroscopy Of the Crsba-15 Materialsmentioning

confidence: 99%

Preparation, Characterization and Catalytic Activity of CrSBA-15 for 2-Propanol Decomposition

Sánchez-Cruz¹,

Hernández-Huesca²,

Pérez-Cruz³

et al. 2020

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The chromium mesoporous materials have been used in many catalytic reactions. Some studies have been devoted to determining the nature of chromium species and to characterizing the chemical structure. The different chromium species depend on synthetic methods and the support used. In this work we prepared mesoporous SBA-15 supported chromium materials referred to in this document as xCrSBA-15, was prepared by the incipient wetness impregnation method. The materials were characterized by X-ray diffraction (XRD), nitrogen (N 2 ) adsorption-desorption isotherms, hydrogen temperature-programmed reduction (H 2 -TPR), scanning electron microscopic (SEM), energy dispersive X-ray spectroscopy (EDS), diffuse reflectance ultraviolet-visible (UV-vis) and Fourier transform IR (FT-IR). Chromium in SBA-15 forms different types of chromates and Cr 2 O 3 , causing morphological and textural changes and generating different catalytic centers. The catalytic conversion of 2-propanol to xCrSBA-15 materials were carried out by in a quartz reactor with a loading of 30 mg of the material at 300°C. Before the catalytic test, the material was activated in two ways: with N 2 and reduced at a H 2 /Ar flow (MxCrSBA-15). The catalytic conversion of 2-propanol to xCrSBA-15 did not increase with reduction (MxCrSBA-15) but decreased deactivation. All the materials had an acidic behavior, which is related to the chromate species in the materials. These results suggest that the more acidic materials favor the formation of coke during the deactivation process, and coke reduces the Cr 3+ to Cr 2+ species, thus decreasing the acidity of the materials.

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Dehydrogenation of Alcohols: Formaldehyde

Dai

Ren

2008

Handbook of Heterogeneous Catalysis

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The sections in this article are Introduction Direct Dehydrogenation of Methanol to Formaldehyde Silver‐Containing Catalysts Copper‐Containing Catalysts Zinc‐Containing Catalysts Other Catalysts Industrial Applications

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Mechanism of dehydrogenation of secondary alcohols on chromia

Cited by 69 publications

References 8 publications

Infrared spectroscopic studies of the reactions of alcohols over group IVB metal oxide catalysts. Part 1.—Propan-2-ol over TiO2, ZrO2 and HfO2

Infrared spectroscopic studies of the reactions of alcohols over group IVB metal oxide catalysts. Part 1.—Propan-2-ol over TiO2, ZrO2 and HfO2

Preparation, Characterization and Catalytic Activity of CrSBA-15 for 2-Propanol Decomposition

Dehydrogenation of Alcohols: Formaldehyde

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