Acid–base properties of supported gallium oxide catalysts

Petre, Alice L.; Auroux, A.; Gélin, P.; Căldăraru, M.; Ionescu, N. I.

doi:10.1016/s0040-6031(01)00615-3

Cited by 62 publications

(27 citation statements)

References 16 publications

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“…It is known that gallium oxide (Ga 2 O 3 ) retains both acid and base properties [18,19]. It has also been reported that gallium oxide supported on metal oxide can modify the acidity and basicity of the support [20].…”

Section: Introductionmentioning

confidence: 99%

Direct Synthesis of Dimethyl Carbonate from Methanol and Carbon Dioxide over Ga2O3/Ce0.6Zr0.4O2 Catalysts: Effect of Acidity and Basicity of the Catalysts

et al. 2011

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Ce X Zr 1-X O 2 catalysts with different cerium content (X) (X = 0, 0.2, 0.4, 0.5, 0.6, 0.8, and 1.0) were prepared by a sol-gel method for use in the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. Among these catalysts, Ce 0.6 Zr 0.4 O 2 was found to show the best catalytic performance. In order to enhance the acidity and basicity of Ce 0.6 Zr 0.4 O 2 catalyst, Ga 2 O 3 was supported on Ce 0.6 Zr 0.4 O 2 (XGa 2 O 3 /Ce 0.6 Zr 0.4 O 2 (X = 1, 5, 10, and 15)) by an incipient wetness impregnation method with a variation of Ga 2 O 3 content (X, wt%). Effect of acidity and basicity of Ga 2 O 3 /Ce 0.6 Zr 0.4 O 2 on the catalytic performance in the direct synthesis of dimethyl carbonate was investigated using NH 3 -TPD and CO 2 -TPD experiments. Experimental results revealed that both acidity and basicity of the catalysts played a key role in determining the catalytic performance in the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. Large acidity and basicity of the catalyst facilitated the formation of dimethyl carbonate. The amount of dimethyl carbonate produced over XGa 2 O 3 /Ce 0.6 Zr 0.4 O 2 catalysts increased with increasing both acidity and basicity of the catalysts. Among the catalysts tested, 5Ga 2 O 3 /Ce 0.6 Zr 0.4 O 2 , which retained the largest acidity and basicity, showed the best catalytic performance in the direct synthesis of dimethyl carbonate from methanol and carbon dioxide.

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Section: Introductionmentioning

confidence: 99%

Direct Synthesis of Dimethyl Carbonate from Methanol and Carbon Dioxide over Ga2O3/Ce0.6Zr0.4O2 Catalysts: Effect of Acidity and Basicity of the Catalysts

et al. 2011

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“…It is generally assumed that significant basicity corresponds to values greater than 80 kJ mol -1 . 31 The concentration of basic sites is related to the amount of SO 2 that adsorbs with enthalpy above this value. However, it…”

Section: Resultsmentioning

confidence: 99%

“…Levels of functionalisation were initially assessed through nitrogen, sulfur and carbon elemental analysis (MEDAC Ltd). To obtain information on the local environment and the degree of condensation of the network, 31 P and 13 C crosspolarization (CP) magic angle spinning (MAS) NMR spectra were collected using a Varian VNMRS 400 spectrometer.…”

Section: Catalyst Characterizationmentioning

confidence: 99%

Environmentally Benign Bifunctional Solid Acid and Base Catalysts

Elmekawy

Shiju

Rothenberg

et al. 2014

Ind. Eng. Chem. Res.

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ABSTRACT:Solid bi-functional acid-base catalysts were prepared in two ways on an amorphous silica support: 1) by grafting mercaptopropyl units (followed by oxidation to propylsulfonic acid) and aminopropyl groups to the silica surface (NH 2 -SiO 2 -SO 3 H), and 2) by grafting only aminopropyl groups and then partially neutralising with phosphotungstic acid, relying on the H 2 PW 12 O 40 -ion for surface acidity (NH 2 -SiO 2 -NH 3 + [H 2 PW 12 O 40 -], denoted as NH 2 -SiO 2 -PTA).Surface acidity and basicity were characterised by adsorption calorimetry, using SO 2 as a probe for surface basicity and NH 3 for surface acidity. Catalytic activities were compared in a two-stage cascade: an acid-catalysed deacetalisation followed directly by a base-catalysed Henry reaction. Overall, the NH 2 -SiO 2 -SO 3 H catalysts showed higher concentrations and strengths of both acid and base sites, and higher activities than NH 2 -SiO 2 -PTA. Both catalysts showed evidence of cooperative acid-base catalysis. Importantly, the bi-functional catalysts exhibited catalytic advantage over physical mixtures of singly functionalised catalysts. 3 INTRODUCTIONMany liquid phase processes in fine chemicals synthesis require acid or base catalysts. Conventionally, homogeneous acids and bases dissolved in the reaction mixtures are used. In most cases, replacing these with solid acids and bases brings substantial environmental benefit by reducing waste and simplifying product separation. 1-3Almost inevitably, however, solid acids and bases are less active than their homogeneous counterparts. Despite this, one case where they might be able to offer particular advantage is where both acid and base catalysis is required, either in sequential steps or through a cooperative catalytic mechanism. A difficulty associated with preparation of the aminopropyl/propylsulfonic acid bi-functional catalysts (NH 2 -SiO 2 -SO 3 H) is that the acid group is grafted to the silica using (3-mercaptopropyl)trimethoxysilane (MPTMS) and an oxidation step is required to convert the thiol (-SH) to sulfonic acid (-SO 3 H). The two main routes reported are based on hydrogen peroxide/sulfuric acid, and on nitric acid (as both oxidant and acidifier). 11,12 The method used must be chosen to effectively oxidise thiol 12 but with minimal reaction with the base groups. Nitric acid has been shown to be the more effective reagent under these conditions 13 so nitric acid is used as the oxidant in the work reported here.An amorphous silica gel has been used as the catalyst support, rather than the ordered SBA-15 silica used in our previous work. Silica gel does not exhibit the friability and low bulk density of SBA-15 14-16 while the surface properties and stability are similar, and it can be functionalised in the same way. The silica gel used here has been chosen to have an average pore diameter similar to that of SBA-15. The tandem deacetalisation-Henry reaction shown in Scheme 2 has been used. The first step is the acid-catalysed deacetalisation of benzaldehyde dimethyl acetal i...

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“…It was inferred that the acidic sites are more predominant. The adsorption of ammonia on supported Ga 2 O 3 is 10 times higher than that of CO 2 [17,18]. The formation of both mono-and bidentate bicarbonate species are formed on coordinatively unsaturated Ga 3+ cations during adsorption of CO 2 on gallium oxide surfaces [19].…”

Section: Introductionmentioning

confidence: 98%

Influence of the Nanostructure of Gallium Oxide Catalysts on Conversion in the Green Synthesis of Carbamates

Shah

Ratnasamy²,

Carreon

2017

Catalysts

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Abstract:The nanostructure of β-gallium oxide crystals influences the conversion to carbamates; specifically, for the synthesis of alkyl carbamates (like propyl N-octylcarbamate) from CO 2 and n-propanol in the absence of phosgene. The nanostructures with variable aspect ratios (length (L)/width (D); from 2 to 18) were prepared by the controlled addition of neutral and cationic surfactants during gallium oxide synthesis. These catalysts displayed selectivities to the corresponding carbamates as high as~70%, superior to non-nanostructured Ga 2 O 3 catalysts. The conversion was found to be inversely proportional to the square of the relative crystallinity. The catalysts retained their structure and catalytic performance upon recycling.

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Acid–base properties of supported gallium oxide catalysts

Cited by 62 publications

References 16 publications

Direct Synthesis of Dimethyl Carbonate from Methanol and Carbon Dioxide over Ga2O3/Ce0.6Zr0.4O2 Catalysts: Effect of Acidity and Basicity of the Catalysts

Direct Synthesis of Dimethyl Carbonate from Methanol and Carbon Dioxide over Ga2O3/Ce0.6Zr0.4O2 Catalysts: Effect of Acidity and Basicity of the Catalysts

Environmentally Benign Bifunctional Solid Acid and Base Catalysts

Influence of the Nanostructure of Gallium Oxide Catalysts on Conversion in the Green Synthesis of Carbamates

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