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Binder Effects in SiO2- and Al2O3-Bound Zeolite ZSM-5-Based Extrudates as Studied by Microspectroscopy.

Whiting GT, Meirer F, Mertens MM, Bons AJ, Weiss BM, Stevens PA, de Smit E, Weckhuysen BM - ChemCatChem (2015)

Bottom Line: It was found that aluminium migration occurs in ZSM-5-containing Al2O3-bound extrudates, forming additional Brønsted acid sites.Not only were the location and distribution of these oligomers visualised by 3 D analysis, it was also observed that more conjugated species appeared to grow off the surface of the zeolite ZSM-5 crystals (containing less conjugated species) into the surrounding binder material.Furthermore, a higher binder content resulted in an increasing overall reactivity owing to the greater number of stored thiophene monomers available per Brønsted acid site.

View Article: PubMed Central - PubMed

Affiliation: Inorganic Chemistry and Catalysis Group, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG, Utrecht (The Netherlands).

ABSTRACT

Microspectroscopic methods were explored to investigate binder effects occurring in ZSM-5-containing SiO2- and Al2O3-bound millimetre-sized extrudates. Using thiophene as a selective probe for Brønsted acidity, coupled with time-resolved in situ UV/Vis and confocal fluorescence microspectroscopy, variations in reactivity and selectivity between the two distinct binder types were established. It was found that aluminium migration occurs in ZSM-5-containing Al2O3-bound extrudates, forming additional Brønsted acid sites. These sites strongly influence the oligomer selectivity, favouring the formation of thiol-like species (i.e., ring-opened species) in contrast to higher oligomers, predominantly formed on SiO2-bound ZSM-5-containing extrudates. Not only were the location and distribution of these oligomers visualised by 3 D analysis, it was also observed that more conjugated species appeared to grow off the surface of the zeolite ZSM-5 crystals (containing less conjugated species) into the surrounding binder material. Furthermore, a higher binder content resulted in an increasing overall reactivity owing to the greater number of stored thiophene monomers available per Brønsted acid site.

No MeSH data available.


Related in: MedlinePlus

Proposed reaction pathway of thiophene oligomerisation on zeolite acid sites. Thiophene monomer (A) undergoes protonation on Brønsted acid sites of H–ZSM‐5 crystals to form the protonated monomer (B). Two different reaction pathways are possible at this stage: opening of the thiophene ring and subsequent reaction with a second monomer to form a thiol‐like carbocation (F1/F1‐T/F2/F2‐T). Alternatively, dimerisation (to C) can occur followed by further oligomerisation (to D) or opening of the thiophene ring, forming a thiol‐like carbocation (F1/F1‐T/F2/F2‐T). The trimeric carbocationic species (D) can undergo further oligomerisation to form more extended/conjugated species (E1/E2).
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sch1: Proposed reaction pathway of thiophene oligomerisation on zeolite acid sites. Thiophene monomer (A) undergoes protonation on Brønsted acid sites of H–ZSM‐5 crystals to form the protonated monomer (B). Two different reaction pathways are possible at this stage: opening of the thiophene ring and subsequent reaction with a second monomer to form a thiol‐like carbocation (F1/F1‐T/F2/F2‐T). Alternatively, dimerisation (to C) can occur followed by further oligomerisation (to D) or opening of the thiophene ring, forming a thiol‐like carbocation (F1/F1‐T/F2/F2‐T). The trimeric carbocationic species (D) can undergo further oligomerisation to form more extended/conjugated species (E1/E2).

Mentions: The selective staining of Brønsted acid sites in a non‐invasive manner has recently been used to study catalyst bodies, such as FCC particles40, 47 and ZSM‐5‐containing SiO2‐bound extrudates.44 Herein we employed thiophene oligomerisation as a probe molecule reaction to study Brønsted acidity variations and binder effects between both ZSM‐5‐containing SiO2‐ and Al2O3‐bound extrudates. As seen in Scheme 1, several carbocations are formed and evidently two reaction pathways take place upon the adsorption and protonation of thiophene monomers: either progressive oligomerisation to form larger more conjugated/extended oligomers (compounds C, D, E) or ring opening to form thiol‐like species (F compounds). In Figure 3 a, the in situ optical absorption spectra (400–700 nm) of a pure ZSM‐5 pellet reacted with thiophene are shown. Owing to the complex nature of the raw absorption spectra obtained (Figure S2), multivariate analysis and time‐dependent density functional theory calculations (on non‐confined molecules) were performed. These were used to fit and tentatively assign the bands formed for each sample’s optical spectra, with the background selectively removed. This procedure and more details can be found in our previous work.44


Binder Effects in SiO2- and Al2O3-Bound Zeolite ZSM-5-Based Extrudates as Studied by Microspectroscopy.

Whiting GT, Meirer F, Mertens MM, Bons AJ, Weiss BM, Stevens PA, de Smit E, Weckhuysen BM - ChemCatChem (2015)

Proposed reaction pathway of thiophene oligomerisation on zeolite acid sites. Thiophene monomer (A) undergoes protonation on Brønsted acid sites of H–ZSM‐5 crystals to form the protonated monomer (B). Two different reaction pathways are possible at this stage: opening of the thiophene ring and subsequent reaction with a second monomer to form a thiol‐like carbocation (F1/F1‐T/F2/F2‐T). Alternatively, dimerisation (to C) can occur followed by further oligomerisation (to D) or opening of the thiophene ring, forming a thiol‐like carbocation (F1/F1‐T/F2/F2‐T). The trimeric carbocationic species (D) can undergo further oligomerisation to form more extended/conjugated species (E1/E2).
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4834610&req=5

sch1: Proposed reaction pathway of thiophene oligomerisation on zeolite acid sites. Thiophene monomer (A) undergoes protonation on Brønsted acid sites of H–ZSM‐5 crystals to form the protonated monomer (B). Two different reaction pathways are possible at this stage: opening of the thiophene ring and subsequent reaction with a second monomer to form a thiol‐like carbocation (F1/F1‐T/F2/F2‐T). Alternatively, dimerisation (to C) can occur followed by further oligomerisation (to D) or opening of the thiophene ring, forming a thiol‐like carbocation (F1/F1‐T/F2/F2‐T). The trimeric carbocationic species (D) can undergo further oligomerisation to form more extended/conjugated species (E1/E2).
Mentions: The selective staining of Brønsted acid sites in a non‐invasive manner has recently been used to study catalyst bodies, such as FCC particles40, 47 and ZSM‐5‐containing SiO2‐bound extrudates.44 Herein we employed thiophene oligomerisation as a probe molecule reaction to study Brønsted acidity variations and binder effects between both ZSM‐5‐containing SiO2‐ and Al2O3‐bound extrudates. As seen in Scheme 1, several carbocations are formed and evidently two reaction pathways take place upon the adsorption and protonation of thiophene monomers: either progressive oligomerisation to form larger more conjugated/extended oligomers (compounds C, D, E) or ring opening to form thiol‐like species (F compounds). In Figure 3 a, the in situ optical absorption spectra (400–700 nm) of a pure ZSM‐5 pellet reacted with thiophene are shown. Owing to the complex nature of the raw absorption spectra obtained (Figure S2), multivariate analysis and time‐dependent density functional theory calculations (on non‐confined molecules) were performed. These were used to fit and tentatively assign the bands formed for each sample’s optical spectra, with the background selectively removed. This procedure and more details can be found in our previous work.44

Bottom Line: It was found that aluminium migration occurs in ZSM-5-containing Al2O3-bound extrudates, forming additional Brønsted acid sites.Not only were the location and distribution of these oligomers visualised by 3 D analysis, it was also observed that more conjugated species appeared to grow off the surface of the zeolite ZSM-5 crystals (containing less conjugated species) into the surrounding binder material.Furthermore, a higher binder content resulted in an increasing overall reactivity owing to the greater number of stored thiophene monomers available per Brønsted acid site.

View Article: PubMed Central - PubMed

Affiliation: Inorganic Chemistry and Catalysis Group, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG, Utrecht (The Netherlands).

ABSTRACT

Microspectroscopic methods were explored to investigate binder effects occurring in ZSM-5-containing SiO2- and Al2O3-bound millimetre-sized extrudates. Using thiophene as a selective probe for Brønsted acidity, coupled with time-resolved in situ UV/Vis and confocal fluorescence microspectroscopy, variations in reactivity and selectivity between the two distinct binder types were established. It was found that aluminium migration occurs in ZSM-5-containing Al2O3-bound extrudates, forming additional Brønsted acid sites. These sites strongly influence the oligomer selectivity, favouring the formation of thiol-like species (i.e., ring-opened species) in contrast to higher oligomers, predominantly formed on SiO2-bound ZSM-5-containing extrudates. Not only were the location and distribution of these oligomers visualised by 3 D analysis, it was also observed that more conjugated species appeared to grow off the surface of the zeolite ZSM-5 crystals (containing less conjugated species) into the surrounding binder material. Furthermore, a higher binder content resulted in an increasing overall reactivity owing to the greater number of stored thiophene monomers available per Brønsted acid site.

No MeSH data available.


Related in: MedlinePlus