scholarly journals Phosphate Enrichment of Niobium-Based Catalytic Surfaces in Relation to Reactions of Carbohydrate Biomass Conversion: The Case Studies of Inulin Hydrolysis and Fructose Dehydration

Catalysts ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1077
Author(s):  
Mariana N. Catrinck ◽  
Sebastiano Campisi ◽  
Paolo Carniti ◽  
Reinaldo F. Teófilo ◽  
Filippo Bossola ◽  
...  
Keyword(s):  
Biomass Conversion ◽  
Acid Sites ◽  
Lewis Acidity ◽  
Total Acidity ◽  
Biomass Hydrolysis ◽  
Inulin Hydrolysis ◽  
Ft Ir ◽  
Fructose Dehydration ◽  
Adsorption Desorption

In this work, some physical mixtures of Nb2O5·nH2O and NbOPO4 were prepared to study the role of phosphate groups in the total acidity of samples and in two reactions involving carbohydrate biomass: hydrolysis of polyfructane and dehydration of fructose/glucose to 5-hydroxymethylfurfural (HMF). The acid and catalytic properties of the mixtures were dominated by the phosphate group enrichment. Lewis and Brønsted acid sites were detected by FT-IR experiments with pyridine adsorption/desorption under dry and wet conditions. Lewis acidity decreased with NbP in the composition, while total acidity of the samples, measured by titrations with phenylethylamine in cyclohexane (~3.5 μeq m−2) and water (~2.7 μeq m−2), maintained almost the same values. Inulin conversion took advantage of the presence of surfaces rich in Brønsted sites, and NbOPO4 showed the best hydrolysis activity with glucose/fructose formation. The catalyst with a more phosphated surface showed less deactivation during the dehydration of fructose/glucose into HMF.

scholarly journals QM/MM Study of the Reactivity of Zeolite Bound Methoxy and Carbene Groups

2021 ◽  
Author(s):  
Andrew Logsdail ◽  
Richard Catlow ◽  
Stefan A. F. Nastase
Keyword(s):  
Acid Site ◽  
Alternative Pathway ◽  
Experimental Studies ◽  
Acid Sites ◽  
Site Formation ◽  
Methanol To Hydrocarbons ◽  
Hydrocarbon Formation ◽  
Autocatalytic Process ◽  
Ft Ir

<div>The conversion of methanol-to-hydrocarbons (MTH) is known to occur via an autocatalytic process in zeolites, where framework-bound methoxy species play a pivotal role, especially during catalyst induction. Recent NMR and FT-IR experimental studies suggest that methoxylated zeolites are able to produce hydrocarbons by a mechanism involving carbene migration and association. In order to understand these observations, we have performed QM/MM computational investigations on a range of reaction mechanisms for the reaction of zeolite bound methoxy and carbene groups, which are proposed to initiate hydrocarbon formation in the MTH process. Our simulations demonstrate that it is kinetically unfavourable for methyl species to form on the framework away from the zeolite acid site, and both kinetically and thermodynamically unfavourable for methyl groups to migrate through the framework and aggregate around an acid site. Formation of carbene moieties was considered as an alternative pathway to the formation of C-C bonds; however, the reaction energy for conversion of a methyl to a carbene is unfavourable. Metadynamics simulations help confirm further that methyl species at the framework acid sites would be more reactive towards formed C<sub>2+</sub> species, rather than inter-framework migration and that the role of carbenes in the formation of the first –C bond will be via a concerted type of mechanism rather than stepwise. </div>

Synergetic effects of Cu-Zn bimetallic ions exchanged in NaX on acid sites of M(x)X zeolites (M = Cu2+ and/or Zn2+, x = level of exchange). An in situ FTIR study using pyridine adsorption/desorption

2019 ◽  
Vol 107 (3) ◽  
pp. 304
Author(s):  
Habib Hammoudi ◽  
Souhila Bendenia ◽  
Isabelle Batonneau-Gener ◽  
Jean-dominique Comparot ◽  
Kheira Marouf-Khelifa ◽  
...  
Keyword(s):  
Synergetic Effect ◽  
Nitrogen Adsorption ◽  
Acid Sites ◽  
Lewis Acidity ◽  
Pyridine Adsorption ◽  
In Situ Ftir ◽  
Desorption Temperature ◽  
X Zeolites ◽  
Adsorption Desorption

X zeolites were prepared by ion-exchange with Cu2+ and/or Zn2+ cations, at different concentrations of the exchange solution, and characterized by thermal analysis and nitrogen adsorption. The acidity of the samples was investigated by pyridine adsorption–desorption followed by in situ Fourier transform infrared (FTIR) spectroscopy. Desorption was carried out at 150, 250 and 350 °C. The objective is to estimate the nature and concentration of acid sites. A comparison between the binary (Cu(x)X, Zn(x)X) and ternary (CuZn(x)X) exchanges was also established (x = level of exchange) through the Cu(43)X, Zn(48)X and CuZn(50)X samples. Lewis acidity decreases overall with desorption temperature and the level of exchange. As the latter increases, there is a conversion of some Lewis sites into those of Brønsted during thermal treatment. In return, the concentration of Brønsted sites increases with the degree of exchange. The Brønsted acidity of CuZn(50)X at 350 °C is more important than the sum of those of Cu(43)X and Zn(48)X with respectively values of 73, 32 and 15 μmol g−1. Besides, the concentration of Brønsted sites for CuZn(50)X increases with desorption temperature. These features indicate the presence of a synergetic effect amplifying the strength of these sites when Cu2+ and Zn2+ cations compete for the occupancy of sites distributed in zeolite cavities.

scholarly journals Synthesis and characterization of zeolite NaX from Bangka Belitung Kaolin as alternative precursor

2018 ◽  
Vol 14 (4) ◽  
pp. 414-418 ◽  
Author(s):  
Vita Nur Iftitahiyah ◽  
Didik Prasetyoko ◽  
Hadi Nur ◽  
Hasliza Bahruji ◽  
Hartati Hartati
Keyword(s):  
Average Pore Size ◽  
Surface Acidity ◽  
Microscopic Analysis ◽  
Acid Sites ◽  
Lewis Acidity ◽  
Zeolite X ◽  
Average Pore ◽  
Zeolite Nax ◽  
Type Iv ◽  
Adsorption Desorption

The potential use of kaolin as silica and alumina precursor for the synthesis of zeolite NaX was investigated in this study. The synthesis involved three steps of reactions; the preparation of seed gel, the formation of feedstock gel using kaolin and the combination of overall gel followed by hydrothermal treatment at 105°C for 12 hours. Analysis using X-ray Diffraction (XRD) method indicated the transformation of kaolin into pure phase zeolite NaX with a small amount of kaolin was still visible. Detail microscopic analysis showed the morphology of zeolite X consisted of octahedral particles with a crystallite diameter of 20-30 µm. Analysis of surface acidity using pyridine as probe molecule indicated the zeolite X has high Brǿnsted acidity with 0.181 mmol/g of acid sites, significantly higher than Lewis acidity ~0.053 mmol/g. The N2 adsorption-desorption measurement indicated a type IV material with both microporous and mesoporous structures with an average pore size of 1.47 nm for micropore and 3.41 nm for mesoporous.

scholarly journals Hierarchical Porous MIL-101(Cr) Solid Acid-Catalyzed Production of Value-Added Acetals from Biomass-Derived Furfural

Polymers ◽  
2021 ◽  
Vol 13 (20) ◽  
pp. 3498
Author(s):  
Shengqi Liu ◽  
Ye Meng ◽  
Hu Li ◽  
Song Yang
Keyword(s):  
Biomass Conversion ◽  
Value Added ◽  
Chlorosulfonic Acid ◽  
Hierarchical Porous ◽  
Acidic Sites ◽  
Metal Organic ◽  
Ft Ir ◽  
Good Catalytic Activity ◽  
Valuable Compounds ◽  
Adsorption Desorption

Considering economic and environmental impacts, catalytic biomass conversion to valuable compounds has attracted more and more attention. Of particular interest is furfural, a versatile biorefinery platform molecule used as a feedstock for the production of fuels and fine chemicals. In this study, the Cr-based metal-organic frameworks (MOFs) MIL-101 were modified by chlorosulfonic acid, and MIL-101 was changed into a hierarchical MOF structure with smaller particles and lower particle crystallinity by CTAB, which significantly improved the acidic sites of the MOFs. The original and modified MIL-101(Cr) catalysts were characterized by XRD, N2 adsorption-desorption, SEM, TEM, and FT-IR. The effects of different catalysts, reaction temperature, catalyst amount, and alcohol type on the reaction were studied. Under the action of the MOFs catalyst, a new mild route for the condensation of furfural with various alkyl alcohols to the biofuel molecules (acetals) was proposed. The conversion route includes the conversion of furfural up to 91% yield of acetal could be obtained within 1 h solvent-free and in room-temperature reaction conditions. The sulfonic acid-functionalized MIL-101(Cr) is easy to recover and reuse, and can still maintain good catalytic activity after ten runs.

scholarly journals Opening up ZSM-5 Hierarchical Zeolite’s Porosity through Sequential Treatments for Improved Low-Density Polyethylene Cracking

Molecules ◽  
2020 ◽  
Vol 25 (12) ◽  
pp. 2878 ◽  
Author(s):  
Karolina A. Tarach ◽  
Kamila Pyra ◽  
Kinga Góra-Marek
Keyword(s):  
Catalytic Cracking ◽  
Product Distribution ◽  
Acid Sites ◽  
Limiting Factors ◽  
Low Density Polyethylene ◽  
Low Density ◽  
Ft Ir ◽  
Sequential Treatments ◽  
Opening Up

An adequately tuned acid wash of hierarchical ZSM-5 zeolites offers a levelling up in the catalytic cracking of low-density polyethylene. Identification of crucial and limiting factors governing the activity of the zeolite was extended with studies about the accessibility of acid sites, nature of the realuminated layer and role of Lewis acid sites. The sequential treatment of a ZSM-5 zeolite offered enhanced activity in low-density polyethylene (LDPE) cracking at low and high conversions, as confirmed by a decrease in the temperatures needed to reach 20% and 80% conversion (T20 and T80, respectively). A linear dependence of the T80 on the coupled IHF (indexed hierarchy factor) and AFB (accessibility factor) highlighted the importance of the textural and acidic parameters in the catalytic cracking of LDPE. Operando FT-IR-GC studies confirmed a higher fraction of short-chain hydrocarbons (C3–C5) in the product distribution of hierarchical catalysts resulting from the effective polymer cracking in easily accessible pores.

Role of the nature of the acid sites in the oxydehydrogenation of propane on a VPO/TiO2 catalyst. An in situ FT-IR spectroscopy investigation

1996 ◽  
Vol 38 (3-4) ◽  
pp. 197-201 ◽  
Author(s):  
L. Savary ◽  
J. Saussey ◽  
G. Costentin ◽  
M. M. Bettahar ◽  
J. C. Lavalley ◽  
...  
Keyword(s):  
Ir Spectroscopy ◽  
Acid Sites ◽  
Tio2 Catalyst ◽  
Ft Ir ◽  
Ft Ir Spectroscopy

scholarly journals QM/MM Study of the Reactivity of Zeolite Bound Methoxy and Carbene Groups

2021 ◽  
Author(s):  
Andrew Logsdail ◽  
Richard Catlow ◽  
Stefan A. F. Nastase
Keyword(s):  
Acid Site ◽  
Alternative Pathway ◽  
Experimental Studies ◽  
Acid Sites ◽  
Site Formation ◽  
Methanol To Hydrocarbons ◽  
Hydrocarbon Formation ◽  
Autocatalytic Process ◽  
Ft Ir

<div>The conversion of methanol-to-hydrocarbons (MTH) is known to occur via an autocatalytic process in zeolites, where framework-bound methoxy species play a pivotal role, especially during catalyst induction. Recent NMR and FT-IR experimental studies suggest that methoxylated zeolites are able to produce hydrocarbons by a mechanism involving carbene migration and association. In order to understand these observations, we have performed QM/MM computational investigations on a range of reaction mechanisms for the reaction of zeolite bound methoxy and carbene groups, which are proposed to initiate hydrocarbon formation in the MTH process. Our simulations demonstrate that it is kinetically unfavourable for methyl species to form on the framework away from the zeolite acid site, and both kinetically and thermodynamically unfavourable for methyl groups to migrate through the framework and aggregate around an acid site. Formation of carbene moieties was considered as an alternative pathway to the formation of C-C bonds; however, the reaction energy for conversion of a methyl to a carbene is unfavourable. Metadynamics simulations help confirm further that methyl species at the framework acid sites would be more reactive towards formed C<sub>2+</sub> species, rather than inter-framework migration and that the role of carbenes in the formation of the first –C bond will be via a concerted type of mechanism rather than stepwise. </div>

scholarly journals On the location of Lewis acidic aluminum in zeolite mordenite and the role of framework-associated aluminum in mediating the switch between Brønsted and Lewis acidity

2021 ◽  
Author(s):  
Manoj Ravi ◽  
Vitaly L. Sushkevich ◽  
Jeroen A. van Bokhoven
Keyword(s):  
Lewis Acid ◽  
Acid Sites ◽  
Lewis Acidity ◽  
Brønsted Acidity ◽  
Lewis Acid Sites ◽  
Brönsted Acidity ◽  
Brønsted And Lewis Acidity

Framework-associated aluminum is demonstrated to facilitate a reversible switch between Lewis and Brønsted acidity in zeolites with the Lewis acid sites preferentially populating the side-pockets in the case of mordenite.

scholarly journals Insight into Active Centers and Anti-Coke Behavior of Niobium-Containing SBA-15 for Glycerol Dehydration

Catalysts ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 488
Author(s):  
Katarzyna Stawicka ◽  
Maciej Trejda ◽  
Maria Ziolek
Keyword(s):  
Coke Formation ◽  
Catalytic Performance ◽  
Acid Sites ◽  
Silica Matrix ◽  
High Concentration ◽  
Active Centers ◽  
Acidic Sites ◽  
Glycerol Dehydration ◽  
Adsorption Desorption ◽  
Insight Into

Niobium containing SBA-15 was prepared by two methods: impregnation with different amounts of ammonium niobate(V) oxalate (Nb-15/SBA-15 and Nb-25/SBA-15 containing 15 wt.% and 25 wt.% of Nb, respectively) and mixing of mesoporous silica with Nb2O5 followed by heating at 500 °C (Nb2O5/SBA-15). The use of these two procedures allowed obtaining materials with different textural/surface properties determined by N2 adsorption/desorption isotherms, XRD, UV-Vis, pyridine, and NO adsorption combined with FTIR spectroscopy. Nb2O5/SBA-15 contained exclusively crystalline Nb2O5 on the SBA-15 surface, whereas the materials prepared by impregnation had both metal oxide and niobium incorporated into the silica matrix. The niobium species localized in silica framework generated Brønsted (BAS) and Lewis (LAS) acid sites. The inclusion of niobium into SBA-15 skeleton was crucial for the achievement of high catalytic performance. The strongest BAS were on Nb-25/SBA-15, whereas the highest concentration of BAS and LAS was on Nb-15/SBA-15 surface. Nb2O5/SBA-15 material possessed only weak LAS and BAS. The presence of the strongest BAS (Nb-25/SBA-15) resulted in the highest dehydration activity, whereas a high concentration of BAS was unfavorable. Silylation of niobium catalysts prepared by impregnation reduced the number of acidic sites and significantly increased acrolein yield and selectivity (from ca. 43% selectivity for Nb-25/SBA-15 to ca. 61% for silylated sample). This was accompanied by a considerable decrease in coke formation (from 47% selectivity for Nb-25/SBA-15 to 27% for silylated material).

scholarly journals Lattice-water-induced acid sites in tungsten oxide hydrate for catalyzing fructose dehydration

2021 ◽  
Vol 149 ◽  
pp. 106254
Author(s):  
Haolin Sun ◽  
Fei Song ◽  
Chunmei Zhou ◽  
Xiaoyue Wan ◽  
Yuguang Jin ◽  
...  
Keyword(s):  
Tungsten Oxide ◽  
Acid Sites ◽  
Oxide Hydrate ◽  
Lattice Water ◽  
Fructose Dehydration
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