Strong Brønsted Acidity in Amorphous Silica−Aluminas

Xu, Bin; Sievers, Carsten; Lercher, Johannes A.; Veen, J.A.R. van; Giltay, Patricia; Prins, R.; Bokhoven, Jeroen A. van

doi:10.1021/jp073677i

Cited by 89 publications

(156 citation statements)

References 32 publications

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“…This may be because of the decrease of Lewis acidity led to the low degree of Diels-Alder cyclization reactions as discussed below. In addition, many works showed that the catalytic dehydrogenation of alkanes like propane and butane to form the gaseous olefins might occur on the Brønsted acid sites [49][50][51]. These results indicated that the formation of olefins strong depends on the Brønsted acid density.…”

Section: Catalytic Conversion Of Soybean Oilmentioning

confidence: 99%

Quantitative conversion of triglycerides to hydrocarbons over hierarchical ZSM-5 catalyst

Chen

Wang

Zhang

et al. 2015

Applied Catalysis B: Environmental

113

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Section: Catalytic Conversion Of Soybean Oilmentioning

confidence: 99%

Quantitative conversion of triglycerides to hydrocarbons over hierarchical ZSM-5 catalyst

Chen

Wang

Zhang

et al. 2015

Applied Catalysis B: Environmental

113

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“…It is classically well known that zeolite has the much higher activity and selectivity for gasoline in the catalytic cracking of heavy hydrocarbons compared with ASA [30]. Further, it was also reported in more recent literature that the catalytic performance for hydrocracking of n-heptane over USY [34] or propane cracking over ZSM-5 [35] was much higher than that for ASA. Although BrØnsted acid sites in ASA might have an intrinsic acidity close to that of zeolites, it was pointed out that the much lower activity for silica-aluminas was due to their very low acid site density [34].…”

mentioning

confidence: 99%

Preparation of hierarchical β and Y zeolite-containing mesoporous silica–aluminas and their properties for catalytic cracking of n-dodecane

Ishihara

Inui

Hashimoto

et al. 2012

Journal of Catalysis

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“…Zeolite-like bridging SiÀ(OH)ÀAl groups are sometimes invoked, [8,9] but are questioned by several other authors. [10,11] Silanols bonded to low-coordinated aluminum atoms by a SiÀOÀAl bridge have been proposed as most acidic Brønsted sites on ASA surfaces, depending on the number and coordination of aluminum atoms.…”

mentioning

confidence: 99%

Acidity of Amorphous Silica–Alumina: From Coordination Promotion of Lewis Sites to Proton Transfer

Chizallet

Raybaud

2010

ChemPhysChem

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Due to their combined Lewis and Brønsted acidities, amorphous silica-alumina (ASA) are widespread supports for multifunctional heterogeneous catalysts in fine chemistry, [1] petrochemical refining [2] and biomass conversion, [3] from the laboratory scale to the industrial plant. [4,5] These materials are moreover suspected in H-USY zeolites.[6] Due to their amorphous nature and despite improvement achieved by magic-angle spinning (MAS) NMR, [7] the local environment of the acid sites remains strongly debated. Zeolite-like bridging SiÀ(OH)ÀAl groups are sometimes invoked, [8,9] but are questioned by several other authors. [10,11] Silanols bonded to low-coordinated aluminum atoms by a SiÀOÀAl bridge have been proposed as most acidic Brønsted sites on ASA surfaces, depending on the number and coordination of aluminum atoms.[12] Trombetta et al.[10] moreover suggested that upon interaction with a basic probe molecule, silanols in the vicinity of threefold-coordinated aluminum atoms could form an additional bond between the oxygen of the silanol and the threefold-coordinated aluminum atom, which is contradicted by Crepeau et al. [12] on the basis of CO adsorption experiments. An open debate thus remains on the identification of the structure of Brønsted sites on ASA surfaces, and on their behavior during the proton transfer step.Earlier, we proposed the first model for ASA surfaces, from periodic density functional theory (DFT) calculations combined with force-field molecular dynamics.[13] Herein, the question of the nature of the Brønsted acid sites on this surface model and of behavior of such sites in the presence of molecules of various basic strengths (CO, pyridine, lutidine and ammonia) is addressed, so as to unravel the origin of the Brønsted acidity of ASA.The ASA periodic surface model was obtained by simulating the contact of g-Al 2 O 3 (100) with a silica film, stable SiÀOH groups being further obtained by gradual hydration of the surface model. The amount and nature of OH groups present on the ASA surface model primarily depends on the temperature and on the water pressure in the reactive medium. For typical reaction temperatures around 200-400 8C and water pressures lower than 1 bar, surface models exhibiting q OH values of 5.4 and 6.4 OH nm À2 can be considered as representative of the real surface state (see the Supporting Information, S1 and S2). Herein, we focus on four relevant sites, depicted in Figure 1.1) For q OH = 6.4 OH mn À2 , a bridging SiÀ(OH)ÀAl site that has a SiÀOÀAl angle of 122.28 (Figure 1 a) is present. Contrary to zeolite-like bridging OH groups, the aluminum atom is pentacoordinated and the hydroxyl exhibits hydrogen-bond donor character. 2) On the surface model with q OH = 5.4 OH mn À2, one silanol bonded to three aluminum atoms (two Al VI and one Al V ) via structural SiÀOÀAl bridges is considered, comparable to the type of sites invoked by CrØpeau et al.[12] (Figure 1 b) with the restriction that Al III (proposed by them) is not stable on our surface model. We call this site Sila...

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Strong Brønsted Acidity in Amorphous Silica−Aluminas

Cited by 89 publications

References 32 publications

Quantitative conversion of triglycerides to hydrocarbons over hierarchical ZSM-5 catalyst

Quantitative conversion of triglycerides to hydrocarbons over hierarchical ZSM-5 catalyst

Preparation of hierarchical β and Y zeolite-containing mesoporous silica–aluminas and their properties for catalytic cracking of n-dodecane

Acidity of Amorphous Silica–Alumina: From Coordination Promotion of Lewis Sites to Proton Transfer

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