scholarly journals Glucose Conversion into 5-Hydroxymethylfurfural over Niobium Oxides Supported on Natural Rubber-Derived Carbon/Silica Nanocomposite

Catalysts ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 887
Author(s):  
Rujeeluk Khumho ◽  
Satit Yousatit ◽  
Chawalit Ngamcharussrivichai
Keyword(s):  
Natural Rubber ◽  
Lewis Acid ◽  
Value Added ◽  
Acid Sites ◽  
Superior Performance ◽  
Lewis Acidity ◽  
Lewis Acid Sites ◽  
Niobium Oxides ◽  
Silica Nanocomposite ◽  
Loading Amount

5-Hydroxymethylfurfural (HMF) is one of the most important lignocellulosic biomass-derived platform molecules for production of renewable fuel additives, liquid hydrocarbon fuels, and value-added chemicals. The present work developed niobium oxides (Nb2O5) supported on mesoporous carbon/silica nanocomposite (MCS), as novel solid base catalyst for synthesis of HMF via one-pot glucose conversion in a biphasic solvent. The MCS material was prepared via carbonization using natural rubber dispersed in hexagonal mesoporous silica (HMS) as a precursor. The Nb2O5 supported on MCS (Nb/MCS) catalyst with an niobium (Nb) loading amount of 10 wt.% (10-Nb/MCS) was characterized by high dispersion, and so tiny crystallites of Nb2O5, on the MCS surface, good textural properties, and the presence of Bronsted and Lewis acid sites with weak-to-medium strength. By varying the Nb loading amount, the crystallite size of Nb2O5 and molar ratio of Bronsted/Lewis acidity could be tuned. When compared to the pure silica HMS-supported Nb catalyst, the Nb/MCS material showed a superior glucose conversion and HMF yield. The highest HMF yield of 57.5% was achieved at 93.2% glucose conversion when using 10-Nb/MCS as catalyst (5 wt.% loading with respect to the mass of glucose) at 190 °C for 1 h. Furthermore, 10-Nb/MCS had excellent catalytic stability, being reused in the reaction for five consecutive cycles during which both the glucose conversion and HMF yield were insignificantly changed. Its superior performance was ascribed to the suitable ratio of Brønsted/Lewis acid sites, and the hydrophobic properties generated from the carbon moieties dispersed in the MCS nanocomposite.

scholarly journals Regenerable Acidity of Graphene Oxide in Promoting Multicomponent Organic Synthesis

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Virgilio D. Ebajo ◽  
Cybele Riesse L. Santos ◽  
Glenn V. Alea ◽  
Yuya A. Lin ◽  
Chun-Hu Chen
Keyword(s):  
Graphene Oxide ◽  
Organic Synthesis ◽  
Lewis Acid ◽  
Photoelectron Spectroscopy ◽  
Acid Sites ◽  
Lewis Acidity ◽  
Epoxide Ring ◽  
Multicomponent Synthesis ◽  
Lewis Acid Sites ◽  
Toxic Reaction

Abstract The Brønsted acidity of graphene oxide (GO) materials has shown promising activity in organic synthesis. However, roles and functionality of Lewis acid sites remain elusive. Herein, we reported a carbocatalytic approach utilizing both Brønsted and Lewis acid sites in GOs as heterogeneous promoters in a series of multicomponent synthesis of triazoloquinazolinone compounds. The GOs possessing the highest degree of oxidation, also having the highest amounts of Lewis acid sites, enable optimal yields (up to 95%) under mild and non-toxic reaction conditions (85 °C in EtOH). The results of FT-IR spectroscopy, temperature-programed decomposition mass spectrometry, and X-ray photoelectron spectroscopy identified that the apparent Lewis acidity via basal plane epoxide ring opening, on top of the saturated Brønsted acidic carboxylic groups, is responsible for the enhanced carbocatalytic activities involving Knoevenagel condensation pathway. Recycled GO can be effectively regenerated to reach 97% activity of fresh GO, supporting the recognition of GO as pseudocatalyst in organic synthesis.

Lewis acid sites in MOFs supports promoting the catalytic activity and selectivity for CO esterification to dimethyl carbonate

2020 ◽  
Vol 10 (6) ◽  
pp. 1699-1707 ◽  
Author(s):  
Yu-Ping Xu ◽  
Zhi-Qiao Wang ◽  
Hong-Zi Tan ◽  
Kai-Qiang Jing ◽  
Zhong-Ning Xu ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Lewis Acid ◽  
Dimethyl Carbonate ◽  
Metal Organic Frameworks ◽  
Acid Sites ◽  
Lewis Acidity ◽  
Catalyst Supports ◽  
Lewis Acid Sites ◽  
Metal Organic

We studied the effect of Lewis acidity in metal–organic frameworks (MOFs) on their activity as catalyst supports for the esterification of CO to dimethyl carbonate.

Influence of Preparation Conditions on the Acidity of WO3/ZrO2 Solid Superacid

2011 ◽  
Vol 233-235 ◽  
pp. 1502-1506 ◽  
Author(s):  
Ping Xu ◽  
Min Wei Wang ◽  
Jia Wei Qu ◽  
Ren Lang Wang ◽  
Jian Wang
Keyword(s):  
Lewis Acid ◽  
Acid Sites ◽  
Acid Strength ◽  
Lewis Acid Sites ◽  
Solid Superacid ◽  
Preparation Conditions ◽  
Acid Type ◽  
Loading Amount ◽  
Superacid Catalysts ◽  
Adsorption Desorption

WO3/ZrO2 solid superacid catalysts were prepared by coprecipitation and impregnation, then were characterized by XRD, N2 adsorption-desorption, Hammett indicator and pyridine chemisorption IR. The acid strength, acid type, acid volume, etc were compared under the different preparation conditions. The results indicated that the catalyst prepared by coprecipitation had stronger acid strength than the catalyst prepared by impregnation. The samples prepared by impregnation had more Lewis acid sites. With the increasing of the W/Zr ratio, the acid strength tended to increase at first and then decrease, and the catalyst with 10% WO3 loading amount had the strongest acidity. The higher the calcination temperature, the less the Lewis acid sites.

scholarly journals Atomically dispersed Lewis acid sites boost 2-electron oxygen reduction activity of carbon-based catalysts

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Qihao Yang ◽  
Wenwen Xu ◽  
Shun Gong ◽  
Guokui Zheng ◽  
Ziqi Tian ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Density Functional ◽  
Density Functional Theory Calculation ◽  
Acid Sites ◽  
Lewis Acidity ◽  
Structure Property ◽  
Lewis Acid Sites ◽  
Hydrogen Electrode ◽  
Voltage Range ◽  
Production Of Hydrogen

Abstract Elucidating the structure-property relationship is crucial for the design of advanced electrocatalysts towards the production of hydrogen peroxide (H2O2). In this work, we theoretically and experimentally discovered that atomically dispersed Lewis acid sites (octahedral M–O species, M = aluminum (Al), gallium (Ga)) regulate the electronic structure of adjacent carbon catalyst sites. Density functional theory calculation predicts that the octahedral M–O with strong Lewis acidity regulates the electronic distribution of the adjacent carbon site and thus optimizes the adsorption and desorption strength of reaction intermediate (*OOH). Experimentally, the optimal catalyst (oxygen-rich carbon with atomically dispersed Al, denoted as O-C(Al)) with the strongest Lewis acidity exhibited excellent onset potential (0.822 and 0.526 V versus reversible hydrogen electrode at 0.1 mA cm−2 H2O2 current in alkaline and neutral media, respectively) and high H2O2 selectivity over a wide voltage range. This study provides a highly efficient and low-cost electrocatalyst for electrochemical H2O2 production.

One-pot transformation of furfural into γ-valerolactone catalyzed by hierarchical Hf-Al-USY zeolite with balanced Lewis and Brønsted acid sites

2021 ◽  
Author(s):  
Bo Tang ◽  
Shuang Li ◽  
Wei-Chao Song ◽  
Yan Li ◽  
En-Cui Yang
Keyword(s):  
Lewis Acid ◽  
Value Added ◽  
Acid Sites ◽  
Bronsted Acid ◽  
Lewis Acid Sites ◽  
One Pot ◽  
Usy Zeolite ◽  
Brønsted Acid Sites ◽  
Brönsted Acid ◽  
Brønsted And Lewis Acid

Upgrading of furfural to high value-added chemicals are currently an attractive and challenging route in biorefineries. Herein, hierarchically structured bifunctional Hf-Al-USY zeolite with balanced Brønsted and Lewis acid sites has...

scholarly journals Effect of Zn/ZSM-5 and FePO4Catalysts on Cellulose Pyrolysis

2015 ◽  
Vol 2015 ◽  
pp. 1-11 ◽  
Author(s):  
Haian Xia ◽  
Xiaopei Yan ◽  
Siquan Xu ◽  
Li Yang ◽  
Yuejie Ge ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Value Added ◽  
Product Distribution ◽  
Acid Sites ◽  
Gas Chromatography Mass Spectrometry ◽  
Lewis Acid Sites ◽  
Liquid Products ◽  
Temperature Programmed ◽  
Xrd Techniques ◽  
Brønsted And Lewis Acid

A series of Zn/ZSM-5 catalysts with different Zn contents and FePO4were used to pyrolyze cellulose to produce value added chemicals. The nature of these catalysts was characterized by ammonia-temperature programmed desorption (NH3-TPD), IR spectroscopy of pyridine adsorption, and X-ray diffraction (XRD) techniques. Noncatalytic and catalytic pyrolytic behaviors of cellulose were studied by thermogravimetric (TG) technique. The pyrolytic liquid products, that is, the biooils, were analyzed by gas chromatography-mass spectrometry (GC-MS). The major components of the biooils are anhydrosugars such as levoglucosan (LGA), 1,6-anhydro-β-D-glucofuranose (AGF), levoglucosenone (LGO, 1,6-anhydro-3,4-dideoxy-β-D-pyranosen-2-one), and 1,4:3,6-dianhydro-α-D-glucopyranose (DGP), as well as furan derivatives, alcohols, and so forth. Zn/ZSM-5 samples with Brønsted and Lewis acid sites and the FePO4catalyst with Lewis acid sites were found to have a significant effect on the pyrolytic behaviors of cellulose and product distribution. These results show that Brønsted and Lewis acid sites modified remarkably components of the biooil, which could promote the production of furan compounds and LGO. On the basis of the findings, a model was proposed to describe the pyrolysis pathways of cellulose catalyzed by the solid acid catalysts.

scholarly journals Catalytic Dehydrofluorination of Hydrofluoroalkanes to Fluorinated Olifein Over Ni/AlF3 Catalysts

2018 ◽  
Vol 238 ◽  
pp. 03004
Author(s):  
Wenzhi Jia ◽  
Xia Cai ◽  
Yong Zhang ◽  
Xiaohua Zuo ◽  
Juanjuan Yuan ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Hydrofluoric Acid ◽  
Catalytic Performance ◽  
Acid Sites ◽  
Lewis Acidity ◽  
Ni Catalyst ◽  
Lewis Acid Sites ◽  
Synergistic Catalysis ◽  
Acidic Catalysts ◽  
Aluminum Compounds

The hydrofluoric acid-resisting aluminum compounds (AlF3, AlPO4, AlN) supported with Ni catalyst were prepared by the wetness impregnation and tested for dehydrofluorination of hydrofluoroalkane to synthesize fluoroolefins. It is found that Ni/AlF3 catalyst has the best catalytic performance, CF3CFH2 conversion of 29.3% after the reaction at 430 °C for 30 h, CF2HCH3 conversion of 31.8% after the reaction at 250 °C for 30 h, respectively. Comparatively, dehydrofluorination temperature of CF3CFH2 is higher than CF2HCH3 over the aluminum compounds catalyst, and the activity of catalysts is related with Lewis acidity. For the aluminum compounds catalyst, addition of Ni had promoted the activity and stability of Lewis acidic catalysts, it is attributed to synergistic catalysis of Lewis acid sites and Ni.

Metal–organic frameworks with Lewis acidity: synthesis, characterization, and catalytic applications

CrystEngComm ◽  
2017 ◽  
Vol 19 (29) ◽  
pp. 4066-4081 ◽  
Author(s):  
Zhigang Hu ◽  
Dan Zhao
Keyword(s):  
Heterogeneous Catalysis ◽  
Lewis Acid ◽  
Metal Organic Frameworks ◽  
Acid Sites ◽  
Lewis Acidity ◽  
Lewis Acid Sites ◽  
Design And Synthesis ◽  
Characterization Techniques ◽  
Metal Organic ◽  
Catalytic Applications

In this highlight, we review the recent development in the design and synthesis of metal–organic frameworks with Lewis acidity, the characterization techniques of Lewis acid sites, and their applications in heterogeneous catalysis.

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.

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