scholarly journals Electronic structure of Lewis acid sites on high surface area aluminium fluorides: a combined XPS and ab initio investigation

2009 ◽  
Vol 11 (27) ◽  
pp. 5664 ◽  
Author(s):  
Anna Makarowicz ◽  
Christine L. Bailey ◽  
Norbert Weiher ◽  
Erhard Kemnitz ◽  
Sven L. M. Schroeder ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Ab Initio ◽  
Surface Area ◽  
Lewis Acid ◽  
High Surface ◽  
High Surface Area ◽  
Acid Sites ◽  
Lewis Acid Sites

scholarly journals High Surface Area VOx/TiO2/SBA-15 Model Catalysts for Ammonia SCR Prepared by Atomic Layer Deposition

Catalysts ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1386
Author(s):  
Jun Shen ◽  
Christian Hess
Keyword(s):  
Atomic Layer Deposition ◽  
Lewis Acid ◽  
High Surface ◽  
High Surface Area ◽  
Atomic Layer ◽  
Acid Sites ◽  
Lewis Acid Sites ◽  
X Ray ◽  
Nox Conversion ◽  
Layer Deposition

The mode of operation of titania-supported vanadia (VOx) catalysts for NOx abatement using ammonia selective catalytic reduction (NH3-SCR) is still vigorously debated. We introduce a new high surface area VOx/TiO2/SBA-15 model catalyst system based on mesoporous silica SBA-15 making use of atomic layer deposition (ALD) for controlled synthesis of titania and vanadia multilayers. The bulk and surface structure is characterized by X-ray diffraction (XRD), UV-vis and Raman spectroscopy, as well as X-ray photoelectron spectroscopy (XPS), revealing the presence of dispersed surface VOx species on amorphous TiO2 domains on SBA-15, forming hybrid Si–O–V and Ti–O–V linkages. Temperature-dependent analysis of the ammonia SCR catalytic activity reveals NOx conversion levels of up to ~60%. In situ and operando diffuse reflection IR Fourier transform (DRIFT) spectroscopy shows N–Hstretching modes, representing adsorbed ammonia and -NH2 and -NH intermediate structures on Bronsted and Lewis acid sites. Partial Lewis acid sites with adjacent redox sites are proposed as the active sites and desorption of product molecules as the rate-determining step at low temperature. The high NOx conversion is attributed to the presence of highly dispersed VOx species and the moderate acidity of VOx supported on TiO2/SBA-15.

scholarly journals Impact of Thermal Treatment of Nb2O5 on Its Performance in Glucose Dehydration to 5-Hydroxymethylfurfural in Water

Nanomaterials ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1685
Author(s):  
Katarzyna Morawa Eblagon ◽  
Anna Malaika ◽  
Karolina Ptaszynska ◽  
Manuel Fernando R. Pereira ◽  
José Luís Figueiredo
Keyword(s):  
Thermal Treatment ◽  
Surface Area ◽  
Pure Water ◽  
High Surface ◽  
High Surface Area ◽  
Acid Sites ◽  
High Ratio ◽  
Total Acidity ◽  
One Pot ◽  
Niobic Acid

The cascade dehydration of glucose to 5-hydroxymethylfurfural (HMF) was carried out in water over a series of Nb2O5 catalysts, which were derived from the thermal treatment of niobic acid at 300 and 550 °C, under air or inert atmosphere. Amorphous niobic acid showed high surface area (366 m2/g) and large acidity (2.35 mmol/g). With increasing the temperature of the thermal treatment up to 550 °C, the amorphous Nb2O5 was gradually transformed into a pseudohexagonal phase, resulting in a decrease in surface area (27–39 m2/g) and total acidity (0.05–0.19 mmol/g). The catalysts’ performance in cascade dehydration of glucose realized in pure water was strongly influenced by the total acidity of these materials. A remarkable yield of 37% HMF in one-pot reaction in water was achieved using mesoporous amorphous niobium oxide prepared by thermal treatment of niobic acid at 300 °C in air. The best-performing catalyst displayed a total acidity lower than niobic acid (1.69 mmol/g) which afforded a correct balance between a high glucose conversion and limited further conversion of the target product to numerous polymers and humins. On the other hand, the treatment of niobic acid at 550 °C, independently of the atmosphere used during the sample preparation (i.e., air or N2), resulted in Nb2O5 catalysts with a high ratio of Lewis to Brønsted acid sites and poor total acidity. These materials excelled at catalyzing the isomerization step in the tandem process.

Identification of possible Lewis acid sites on the β-AlF3(100) surface: an ab initio total energy study

2005 ◽  
Vol 7 (23) ◽  
pp. 3989 ◽  
Author(s):  
Adrian Wander ◽  
Christine L. Bailey ◽  
Barry G. Searle ◽  
Sanghamitra Mukhopadhyay ◽  
Nicholas M. Harrison
Keyword(s):  
Total Energy ◽  
Ab Initio ◽  
Lewis Acid ◽  
Acid Sites ◽  
Lewis Acid Sites

scholarly journals Furfural Hydrogenation on Modified Niobia

2019 ◽  
Vol 9 (11) ◽  
pp. 2287 ◽  
Author(s):  
Andrea Jouve ◽  
Stefano Cattaneo ◽  
Daniel Delgado ◽  
Nicola Scotti ◽  
Claudio Evangelisti ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Lewis Acid ◽  
Furfuryl Alcohol ◽  
Surface Acidity ◽  
High Surface ◽  
Pt Nanoparticles ◽  
Acid Sites ◽  
High Catalytic Activity ◽  
Lewis Acid Sites ◽  
Furfural Hydrogenation

In this study, niobia-based materials have been used as supports for Pt nanoparticles and used in the hydrogenation of furfural. The incorporation of dopants (W6+ and Ti4+) in the Nb2O5 structure induced modifications in the surface acidity of the support; in particular, the addition of W6+ increased the amount of Lewis acid sites, while the addition of Ti4+ decreased the number of Lewis acid sites. As a result, the catalytic activity towards the hydrogenation of furfural was affected; high surface acidity resulted in high catalytic activity. The selectivity of the reaction changed with the support acidity as well, with higher amount of furfuryl alcohol produced decreasing the Lewis acid sites.

scholarly journals Characterization of Lewis acid sites on the (100) surface of β-AlF3: Ab initio calculations of NH3 adsorption

2008 ◽  
Vol 128 (22) ◽  
pp. 224703 ◽  
Author(s):  
C. L. Bailey ◽  
A. Wander ◽  
S. Mukhopadhyay ◽  
B. G. Searle ◽  
N. M. Harrison
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Lewis Acid ◽  
Acid Sites ◽  
Lewis Acid Sites ◽  
Nh3 Adsorption

scholarly journals Acylation of Anisole With Benzoyl Chloride Over Rapidly Synthesized Fly Ash–Based HBEA Zeolite

2021 ◽  
Vol 9 ◽  
Author(s):  
Alechine E. Ameh ◽  
Nicholas M. Musyoka ◽  
Oluwaseun Oyekola ◽  
Benoit Louis ◽  
Leslie F. Petrik
Keyword(s):  
Fly Ash ◽  
Hydrothermal Synthesis ◽  
Surface Area ◽  
Benzoyl Chloride ◽  
High Surface ◽  
High Surface Area ◽  
Strong Acid ◽  
Acid Sites ◽  
Synthesis Time ◽  
Strong Acid Sites

Stable HBEA zeolite with high surface area and strong acid sites was synthesized from coal fly ash–based silica extract via indirect hydrothermal synthesis. The rapid HBEA hydrothermal crystallization times of 8, 10, and 12 h were achieved through a reduced molar water fraction in the synthesis composition. The HBEA zeolites prepared from fly ash silica extract exhibited well-defined spheroidal-shaped crystal morphology with uniform particle sizes of 192, 190, or 239 nm obtained after 8, 10, or 12 h of synthesis time, respectively. The high surface area and the microporous area of 702 and 722 m2/g were achieved as a function of shorter hydrothermal synthesis durations (10 and 24 h, respectively) compared to 48 or 72 h, which resulted in HBEA zeolites with lower surface areas of 538 and 670 m2/g. Likewise, temperature-programmed desorption measurements of fly ash–based HBEA zeolites revealed the presence of weak and strong acid sites in the zeolite. The submicron crystal sizes with a well-defined porosity of HBEA zeolites enhanced the diffusion of anisole and benzoyl chloride molecules toward the active acid sites and hence showed better conversion and selectivity in acylation products. High conversion of benzoyl chloride with anisole was achieved, reaching up to 83% with a 93–96% selectivity toward 4-methoxyacetophenone.

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