Surface acidity, catalytic activity and selectivity of some oxides supported on alumina

Yori, Juan Carlos; Luy, J.C.; Parera, J.M.

doi:10.1016/s0166-9834(00)80377-2

Cited by 13 publications

(5 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In particular, the catalytic conversion of simple organic molecules such as isopropanol has often been used to probe ASA active sites, but the mechanisms of these reactions have been scarcely studied. Thus far, the nature of the active sites for alcohol dehydration has not be unambiguously related to either Brønsted or Lewis acidity, making the interpretation of catalytic measurements challenging.…”

Section: Figurementioning

confidence: 99%

“…However,the difficulty is to link sites singled out by spectroscopic measurements and DFT calculations to the catalytic activity of ASAs.A saconsequence,t he exact nature of the sites responsible for the ASA activity in agiven reaction remains strongly debated in the literature.I n particular,t he catalytic conversion of simple organic molecules such as isopropanol has often been used to probe ASA active sites, [18] but the mechanisms of these reactions have been scarcely studied. Thus far, the nature of the active sites for alcohol dehydration has not be unambiguously related to either Brønsted [19][20][21][22] or Lewis acidity, [23,24] making the interpretation of catalytic measurements challenging.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Isopropanol Dehydration on Amorphous Silica–Alumina: Synergy of Brønsted and Lewis Acidities at Pseudo‐Bridging Silanols

et al. 2016

View full text Add to dashboard Cite

The mechanism of isopropanol dehydration on amorphous silica-alumina (ASA) was unraveled by ac ombination of experimental kinetic measurements and periodic density functional theory (DFT) calculations.W es how that pseudo-bridging silanols (PBS-Al) are the most likely active sites owingt ot he synergy between the Brønsted and Lewis acidic properties of these sites,which facilitates the activation of alcohol hydroxy groups as leaving groups.I sopropanol dehydration was used to specifically investigate these PBS-Al sites,whose density was estimated to be about 10 À1 site nm À2 on the silica-doped alumina surface under investigation, by combining information from experiments and theoretical calculations.

show abstract

Section: Figurementioning

confidence: 99%

mentioning

confidence: 99%

Isopropanol Dehydration on Amorphous Silica–Alumina: Synergy of Brønsted and Lewis Acidities at Pseudo‐Bridging Silanols

et al. 2016

View full text Add to dashboard Cite

show abstract

“…In addition, acid strength and strength distribution are important aspects for a complete knowledge of the acidity of solids. The most important and widespread used techniques are temperature-programmed desorption − and infrared spectroscopy. ,,− However, an ideal technique able to furnish an exhaustive knowledge of the acid character of solids is not known. A combination of techniques can provide a comprehensive picture of the solid acidity in terms of their nature (Brönsted or Lewis sites), number, and ultimately their strength and strength distribution. − …”

Section: Introductionmentioning

confidence: 99%

Acidic Character of Metal-Loaded Amorphous and Crystalline Silica−Aluminas Determined by XPS and Adsorption Calorimetry

1999

View full text Add to dashboard Cite

The XPS technique in combination with microcalorimetry was used to picture the acid character of metal ion loaded zeolite and silica-alumina samples. Co, Cu, and Ni ions were loaded on ZSM-5 and SiO 2 -Al 2 O 3 (about 1 mmol/g) by three different procedures: ion exchange, impregnation, and solid-state ion-exchange. The samples prepared by ion exchange of the two matrixes presented high values of the 2 p 3/2 XPS bands of the metal ions, indicating the occurrence of charge transfer from the ions to the support matrix. This permitted the stabilization of the metal phases as isolated ions rather than as oxide clusters. Microcalorimetric experiments of ammonia adsorption were performed in order to determine the number, strength (i.e., adsorption enthalpy), and strength distribution of the acid sites on the samples and on the relevant matrixes. The N 1s XPS lines of ammonia adsorbed on the surfaces were decomposed into two component peaks, assigned to Brönsted (average value of BE, 402.2 eV) and Lewis (average value of BE, 400.4 eV) acid sites. The relative intensities of the two peak components were measured for the quantitative determination of Brönsted and Lewis acid site concentrations. Coupling the information from adsorption calorimetry and XPS spectroscopy of N 1s adsorbed lines, the absolute numbers of Brönsted and Lewis acid sites on each sample were determined. The two support matrixes were protonic acids (65 and 60% of Brönsted acid sites for ZSM-5 and SiO 2 -Al 2 O 3 , respectively), and the acidity of ZSM-5 was greater than that of SiO 2 -Al 2 O 3 considering both the number of total acid sites and the acid strength. The presence of metal ions deposited on the two matrixes deeply changed the respective proportions of Brönsted and Lewis sites. A huge increase in the Lewis acid site population of the ZSM-5-based samples (70, 85, and 90% of Lewis sites for the samples containing Co, Cu, and Ni, respectively) and of the SiO 2 -Al 2 O 3 -based samples prepared by ion exchange (55, 60, and 70% of Lewis sites for the samples containing Co, Cu, and Ni, respectively) was observed.

show abstract

“…Therefore USY was not considered further. Despite showing the lowest hydrogenolysis activity in Table 1 (entry 8), mordenite is prone to fast deactivation (Figure S10), which has been ascribed by several groups to coke formation blocking the pores [15,18,26–28] . Indeed, the unidirectional pore system of the MOR topology is highly susceptible to obstruction of the channels, making large portions of the active sites unavailable for catalysis [29,30] .…”

Section: Resultsmentioning

confidence: 99%

“…A time‐on‐stream experiment was run using the 0.1 wt % Pt/OSDA‐free Beta catalyst, with a H 2 / n‐ C 4 ratio of 97.5 : 2.5. Hydrogen has been shown to hinder coke formation and so slows down the rate of catalyst deactivation [17,26,27] . The plot in Figure S11 shows that after an initial decline of a few %, the conversion stayed constant for at least 15 h. Finally, we also addressed the regeneration and reuse of the catalyst (Table 8).…”

Section: Resultsmentioning

confidence: 99%

Butane Hydroisomerisation Using Pt‐Promoted OSDA‐Free Zeolite Beta

et al. 2023

View full text Add to dashboard Cite

Hydroisomerisation of n‐butane to isobutane is a challenging reaction, even for Pt‐loaded zeolites with strong acid sites. In comparison with 10‐membered ring (10MR) zeolites, 12‐membered ring (12MR) zeolites give consistently higher isomerisation yields. We report that besides the known catalysts with *BEA topology, also three‐dimensional frameworks with MSE and YFI topologies (with Si/Al∼10) are suitable to obtain high isobutane selectivities and yields. As an alternative to Beta zeolites obtained via templated synthesis, Beta zeolites prepared via a template‐free synthesis proved to be more active at lower temperatures and delivered higher isobutane yields in such conditions. Side reactions such as the Pt‐catalysed hydrogenolysis were successfully suppressed by decreasing the Pt content, even in hydrogen‐rich conditions. Isobutane yields up to 31 % were achieved in a single pass.

show abstract

Surface acidity, catalytic activity and selectivity of some oxides supported on alumina

Cited by 13 publications

References 16 publications

Isopropanol Dehydration on Amorphous Silica–Alumina: Synergy of Brønsted and Lewis Acidities at Pseudo‐Bridging Silanols

Isopropanol Dehydration on Amorphous Silica–Alumina: Synergy of Brønsted and Lewis Acidities at Pseudo‐Bridging Silanols

Acidic Character of Metal-Loaded Amorphous and Crystalline Silica−Aluminas Determined by XPS and Adsorption Calorimetry

Butane Hydroisomerisation Using Pt‐Promoted OSDA‐Free Zeolite Beta

Contact Info

Product

Resources

About