Etude par spectroscopie infrarouge de la coordination et de l'adsorption de (CD3)2CHOH. I - coordination avec des acides de lewis

Gallas, J.P.; Binet, Claude

doi:10.1016/0378-4487(82)80045-9

Cited by 9 publications

(1 citation statement)

References 27 publications

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“…In this latter case, it is well known that coordination increases the strength of the alcohol proton acidity, explaining the formation of 1.2 complex. 45 The greater the strength of Lewis acidity, the greater should be the acidity of the proton, explaining why only the strongest Lewis acid sites would be active. In the case of a dissociative adsorption, it has been shown that acidic alcohols can promote the conversion of an acidic test reaction such as but-l-ene isomerization on alumina.46 It was explained by inductive effects from the alkoxy group to the neighbouring hydrogen.…”

Section: Discussionmentioning

confidence: 99%

Acidic and basic properties of titania–alumina mixed oxides; active sites for propan-2-ol dehydration

Lahousse¹,

Maugé²,

Bachelier³

et al. 1995

J. Chem. Soc., Faraday Trans.

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Ti0,-AI,O, mixed oxides have been prepared by cohydrolysis of Ti4' and A13+ isopropoxides, Textural and acid-base properties were investigated using nitrogen physisorption, adsorption of probe molecules followed by FTIR spectroscopy, and test-reactions. Catalysts were found to exhibit high surface areas and pore volumes. Results obtained from adsorbed CO, probe molecules and COS hydrolysis activity agreed well and showed that the hydroxy basicity of mixed oxides was lower than that of t h e two oxide components. Pyridine and 2,6-dimethylpyridine were used to titrate Lewis and Brsnsted acidic sites, respectively. A linear inerease of t h e number of strong Lewis acid sites with alumina content was observed, whereas t h e number of Br0nsted acid sites reached a maximum for 30% Ti0,-70% AI,O, compared with that expected from t h e composition and t h e activity of pure oxides. Comparison between probe-molecule adsorption and test reaction, points out that both types of site are involved in propan-2-01 dehydration. A transformation of Lewis acid sites into Bransted sites is proposed when propan-2-01 is chemisorbed on Lewis acid sites.Mixed oxides are increasingly used in catalysis because they can present properties different from those of the component single-metal oxides. A typical case is that of silica-alumina. In a recent paper, we examined the acidic and basic properties of Zr0,-Al,O, and Zr0,-TiO, mixed oxides using adsorption of specific probe molecules followed by FTIR, and activity towards two test-reactions : propan-2-01 dehydration and carbon oxysulfide hydrolysis.2 This work concerns Ti0,-A1203 mixed oxides. Our aim was not only to determine their acidic and basic properties but also to correlate probe adsorption and catalytic activities in order to specify the nature of the active sites. For this we chose test reactions with well characterized basicity and acidity. The mechanism of COS hydrolysis is now well e~tablished.~ In particular, the active sites are basic hydroxy groups, also involved in CO, adsorption in the form of hydrogen carbonate species, explaining the good correlation between catalyst activity and the 6(OH) band intensity of HOCO, -~p e c i e s .~ Conversely, propan-2-01 dehydration is largely used as an acidity test, but the nature of its active sites is more complex. Indeed, catalytic activity of Zr0,-TiO, mixed oxides was found to follow Bransted acid sites detected by 2,6-dimethylpyridine (lutidine), whereas for Zr0,-Al,O, activity seemed to be determined by the strong A13 + Lewis acidity, evidenced by pyridine.* Owing to the presence of strong Lewis acidity on pure Al,O, and some Brarnsted acidity on pure TiO,, Al,O,-TiO, mixed oxides are expected to present both types of active site and are therefore interesting model catalysts.It has recently been reported that use in hydrotreatment reactions of TiO,-Al,O, as supports for molybdenum sulfided catalysts, increases the specific rate for hydrodesulfurization of t h i~p h e n e .~ Moreover, McVicker and Ziemiak showed that these mixed ...

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Section: Discussionmentioning

confidence: 99%