Abstract:Biomass-derived 2-methyltetrahydrofuran (2-MTHF) undergoes tandem ring-opening and dehydration (dehydra-decyclization) to linear pentadienes, namely 1,3-pentadiene and 1,4-pentadiene. It can also fragment to butenes and formaldehyde through a competing retro-Prins condensation pathway. Using detailed kinetic measurements of 2-MTHF dehydra-decyclization on zeolites with disparate acidities (boro- and alumino-silicates) and micropore environments (MFI, MWW, and BEA), weakly acidic borosilicates were show… Show more
“…We note that similar proton/heteroatom values have been previously reported on other weakly Brønsted acidic materials (e.g. H + /Xbulk in the range ~ 0.1-0.25 for B-MFI) 5,6 and it follows from the discussion that a majority of phosphorus in P-SPP is inactive for IPA dehydration/Hofmann elimination chemistries. However, within the limitations of this technique, this analysis allows for a reasonable comparison of phosphorous containing materials and aluminosilicate per active site.…”
Section: Ipa + Pyridinesupporting
confidence: 87%
“…The reported samples vary from purely microporous (P-MFI and P-BEA), purely mesoporous (P-MCM-41), micro-and mesoporous (P-SBA-15 and P-SPP) to non-porous (P-Stöber); the bulk phosphorous content was held relatively constant across all materials (Si/P ~ 30). Correponding data for the aluminosilicate zeolite samples has been previously reported in our prior works: ZSM-5 (Si/Al 40 and 140)), 5,24 Al-BEA (Si/Al 12.5), 5 and Al-SPP (Si/Al 62) 25 and not discussed here for brevity.…”
Section: Synthesis and Characterization Of P-zeosilssupporting
confidence: 62%
“…1,2,4 One strategy to address these issues has involved the tuning of solid Brønsted site strength in zeolites to selectively promote desirable pathways, and has relied on the catalytic investigations of trivalent-atom-substituted ([Ga], [Fe], and [B]) zeolites. 5,6 Alternatively, our recent work on exploring selective dehydration catalysts has led to the development of phosphoric-acid supported on all-silica zeolites (with Si/P >10). [7][8][9] For example, phosphoric acid impregnated on selfpillared pentasil (P-SPP) 10 led to the suppression of Abstract.…”
The acid sites of phosphorus-containing zeosils were probed through a combination of solid acid characterization, density functional theory calculations, and kinetic interrogations, establishing their weakly Brønsted acidic character. Due to the disparity in acid-site strength, P-zeosils catalyzed the probe chemistry of isopropanol dehydration slower than aluminosilicate zeolites by an order of magnitude on an active site basis. Propene selectivity during isopropanol dehydration remained 20-30% higher than that of aluminosilicates, illustrating the distinct nature of the weakly acidic phosphorus active sites that favored unimolecular dehydration routes. Regardless of the confining siliceous environment, the nature of phosphorous active sites was unchanged, indicated by identical apparent uni- and bi-molecular dehydration energy barriers. Kinetic isotope experiments with deuterated isopropanol feeds implicated an E2-type elimination to propene formation on phosphorus-containing materials. Comparison of KIEs between phosphorus-containing zeosils and aluminosilicates pointed to an unchanged isopropanol dehydration mechanism, with changes in apparent energetic barriers attributed to weaker binding on phosphorous-active sites that lead to a relatively destabilized alcohol dimer adsorbate. Both ex-situ alkylamine Hofmann elimination and in-situ pyridine titration characterization methods exhibited phosphorous acid site counts dependent on probe molecules identity and/or concentration, underpinning the limitations of extending common characterization techniques for Brønsted-acid catalysis to weakly acidic materials.
“…We note that similar proton/heteroatom values have been previously reported on other weakly Brønsted acidic materials (e.g. H + /Xbulk in the range ~ 0.1-0.25 for B-MFI) 5,6 and it follows from the discussion that a majority of phosphorus in P-SPP is inactive for IPA dehydration/Hofmann elimination chemistries. However, within the limitations of this technique, this analysis allows for a reasonable comparison of phosphorous containing materials and aluminosilicate per active site.…”
Section: Ipa + Pyridinesupporting
confidence: 87%
“…The reported samples vary from purely microporous (P-MFI and P-BEA), purely mesoporous (P-MCM-41), micro-and mesoporous (P-SBA-15 and P-SPP) to non-porous (P-Stöber); the bulk phosphorous content was held relatively constant across all materials (Si/P ~ 30). Correponding data for the aluminosilicate zeolite samples has been previously reported in our prior works: ZSM-5 (Si/Al 40 and 140)), 5,24 Al-BEA (Si/Al 12.5), 5 and Al-SPP (Si/Al 62) 25 and not discussed here for brevity.…”
Section: Synthesis and Characterization Of P-zeosilssupporting
confidence: 62%
“…1,2,4 One strategy to address these issues has involved the tuning of solid Brønsted site strength in zeolites to selectively promote desirable pathways, and has relied on the catalytic investigations of trivalent-atom-substituted ([Ga], [Fe], and [B]) zeolites. 5,6 Alternatively, our recent work on exploring selective dehydration catalysts has led to the development of phosphoric-acid supported on all-silica zeolites (with Si/P >10). [7][8][9] For example, phosphoric acid impregnated on selfpillared pentasil (P-SPP) 10 led to the suppression of Abstract.…”
The acid sites of phosphorus-containing zeosils were probed through a combination of solid acid characterization, density functional theory calculations, and kinetic interrogations, establishing their weakly Brønsted acidic character. Due to the disparity in acid-site strength, P-zeosils catalyzed the probe chemistry of isopropanol dehydration slower than aluminosilicate zeolites by an order of magnitude on an active site basis. Propene selectivity during isopropanol dehydration remained 20-30% higher than that of aluminosilicates, illustrating the distinct nature of the weakly acidic phosphorus active sites that favored unimolecular dehydration routes. Regardless of the confining siliceous environment, the nature of phosphorous active sites was unchanged, indicated by identical apparent uni- and bi-molecular dehydration energy barriers. Kinetic isotope experiments with deuterated isopropanol feeds implicated an E2-type elimination to propene formation on phosphorus-containing materials. Comparison of KIEs between phosphorus-containing zeosils and aluminosilicates pointed to an unchanged isopropanol dehydration mechanism, with changes in apparent energetic barriers attributed to weaker binding on phosphorous-active sites that lead to a relatively destabilized alcohol dimer adsorbate. Both ex-situ alkylamine Hofmann elimination and in-situ pyridine titration characterization methods exhibited phosphorous acid site counts dependent on probe molecules identity and/or concentration, underpinning the limitations of extending common characterization techniques for Brønsted-acid catalysis to weakly acidic materials.
“…Other typical side products are propene and large aromatics (C6+ fraction). 41 Scheme 1 Known Reaction Pathways for the Brønsted Acid Catalyzed Dehydration of Ethanol, 2-Propanol, 1-Butanol, and Dehydra-Decyclization of 2-Methyltetrahydrofuran …”
This work describes the design and implementation of an automated device for catalytic materials testing by direct modifications to a gas chromatograph (GC). The setup can be operated as a plug-flow isothermal reactor and enables the control of relevant parameters such as reaction temperature and reactant partial pressures directly from the GC. High-quality kinetic data (including reaction rates, product distributions, and activation barriers) can be obtained at almost one-tenth of the fabrication cost of analogous commercial setups. With these key benefits including automation, low cost, and limited experimental equipment instrumentation, this implementation is intended as a high-throughput catalyst screening reactor that can be readily utilized by materials synthesis researchers to assess the catalytic properties of their synthesized structures in vapor-phase chemistries.
“…The advantages that allow the applicability of these materials derive mainly from their acidic properties: distribution of strong (Brønsted) and weak (Lewis) sites. Thus, aiming to increase acidity in a controlled way, the introduction of heteroatoms with valences equal to or close to those that normally exist in these materials allows optimizations ranging from the possibility of new applications to the discovery of new structures 3,4 .…”
Silicoaluminophosphates SAPO-5 and SAPO-11 were synthesized using the hydrothermal method, 170 ºC with triethylamine and dipropylamine as the structure directing agents, respectively. This work aimed the incorporation of boron into the structures obtained by modifying the composition of the system, using as a reaction equation: Al 2 O 3 :P 2 O 5 :x SiO 2 : yB 2 O 3 :1,5TEA (or DPA):50H 2 O, with x, y=0-0.2. The phase was identified by XRD and characterized by FTIR, TGA/DTG, TPD-NH 3 and nitrogen adsorption at -196°C. The structure parameters confirmed the obtaining of pure structures, showing a slight contraction in the parameters of the unit cells, indicating the presence of boron in the crystal lattice. The Brønsted sites, were modified up to a maximum of boron (y = 0.1) and for higher content, the acidity was not significant. The modification of weak acidity related to the appearance of isolated BO 3 groups, indicating that the silicon atoms were not sufficiently distributed for the formation of sites.
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