scholarly journals Pore Blocking by Phenolates as Deactivation Path during the Cracking of 4-Propylphenol over ZSM-5

Catalysts ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 721
Author(s):  
Michael J. Stellato ◽  
Giada Innocenti ◽  
Andreas S. Bommarius ◽  
Carsten Sievers
Keyword(s):  
Model Compound ◽  
Acid Sites ◽  
Light Olefins ◽  
Lewis Acid Sites ◽  
Zeolite Framework ◽  
Pore Blocking ◽  
Spent Catalysts ◽  
Cracking Process ◽  
Comprehensive Characterization

Cracking of propyl side chains from 4-propylphenol, a model compound for lignin monomers, is studied for a commercial ZSM-5 zeolite catalyst. The decline of 4-propylphenol conversion with time on stream can be delayed by co-feeding water. FTIR spectroscopy shows the formation of chemisorbed phenolates during reactions and significant amounts of phenolics are detected by GC-MS of the extract from the spent catalysts. Thus, chemisorbed phenolates are identified as the main reason for deactivation in the absence of water. Regardless of the amount of co-fed water, substituted monoaromatics and polyaromatic species are formed. Comprehensive characterization of the spent catalysts including Raman and solid-state 27Al NMR spectroscopy, and thermogravimetric analysis points to a combination of deactivation processes. First, phenolates bind to Lewis acid sites within the zeolite framework and hinder diffusion unless they are hydrolyzed by water. In addition, light olefins created during the cracking process react to form a polyaromatic coke that deactivates the catalyst more permanently.

Enhancing Brønsted and Lewis Acid Sites of the Utilized Spent RFCC Catalyst Waste for the Continuous Cracking Process of Palm Oil to Biofuels

2020 ◽  
Vol 59 (20) ◽  
pp. 9459-9468 ◽  
Author(s):  
I. Istadi ◽  
Teguh Riyanto ◽  
Luqman Buchori ◽  
Didi Dwi Anggoro ◽  
G. Gilbert ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Palm Oil ◽  
Acid Sites ◽  
Lewis Acid Sites ◽  
Cracking Process ◽  
Brønsted And Lewis Acid

Sol-Gel Preparation and Characterization of Niobia thin Films for Catalytic Sensor Applications

1994 ◽  
Vol 346 ◽  
Author(s):  
Rosibel Ochoa ◽  
Raul Miranda
Keyword(s):  
Thin Films ◽  
Gas Sensors ◽  
Sol Gel ◽  
Acid Sites ◽  
Lewis Acid Sites ◽  
Sensor Applications ◽  
Donor Acceptor ◽  
Gel Preparation ◽  
Niobium Ethoxide

ABSTRACTThin films of niobium pentoxide were deposited on quartz plates by spin-coating a solution of niobium ethoxide in ethanol. The films were tested as potential selective gas sensors by exposing them to various reducing environments. It was found that they were selective and sensitive to ammonia. This sensitivity was attributed to the formation of donor-acceptor complexes between chemisorbed ammonia and Lewis acid sites on the solid.

scholarly journals Catalytic Deactivation of HY Zeolites in the Dehydration of Glycerol to Acrolein

Catalysts ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 360
Author(s):  
Israel Pala-Rosas ◽  
José L. Contreras ◽  
José Salmones ◽  
Beatriz Zeifert ◽  
Ricardo López-Medina ◽  
...  
Keyword(s):  
Acid Sites ◽  
Molar Ratio ◽  
Lewis Acid Sites ◽  
Glycerol Conversion ◽  
Molar Ratios ◽  
Surface Areas ◽  
Large Mesopores ◽  
Hy Zeolites ◽  
Catalytic Deactivation

The study of the deactivation of HY zeolites in the dehydration reaction of glycerol to acrolein has represented a challenge for the design of new catalysts. HY zeolites with SiO2/Al2O3 molar ratios between 3.5 and 80 were studied. The solids were characterized by XRD, N2 physisorption, SEM-EDXS, Raman and UV-vis spectroscopies, infrared spectroscopy of pyridine (FTIR-Py) and catalytic activity tests from 250 °C to 325 °C. It was found that the total amount of acid sites per unit area of catalyst decreased as the SiO2/Al2O3 molar ratio increased from 3.5 to 80, resulting in the decrease in the initial glycerol conversion. The initial acrolein selectivity was promoted with the increase of the Brønsted/Lewis acid sites ratio at any reaction temperature. The deactivation tests showed that the catalyst lifetime depended on the pore structure, improving with the presence of large surface areas as evidenced by the deactivation rate constants. The characterization of the deactivated catalysts by XRD, N2 physisorption and thermogravimetric analysis indicated that the deposition of coke resulted in the total obstruction of micropores and the partial blockage of mesopores. Moreover, the presence of large mesopores and surface areas allowed the amount of coke deposited at the catalyst surface to be reduced.

Unraveling the ultrafast behavior of nile red interacting with aluminum and titanium co-doped MCM41 materials

2016 ◽  
Vol 18 (3) ◽  
pp. 2152-2163 ◽  
Author(s):  
Cristina Martin ◽  
Boiko Cohen ◽  
María Teresa Navarro ◽  
Avelino Corma ◽  
Abderrazzak Douhal
Keyword(s):  
Lewis Acid ◽  
Nile Red ◽  
Acid Sites ◽  
Lewis Acid Sites ◽  
Brønsted And Lewis Acid ◽  
Co Doped

Spectroscopic and photodynamic characterization of Nile Red during interaction with Brønsted and Lewis acid sites within single- and multi-metal(X)-doped MCM41 materials (X = Ti and/or Al).

Characterization of Lewis-acid sites in zeolites by EPR using the NO molecule as a probe

1996 ◽  
Vol 92 (13) ◽  
pp. 2495 ◽  
Author(s):  
Aleksander Gutsze ◽  
Martin Plato ◽  
Hellmut G. Karge ◽  
Frank Witzel
Keyword(s):  
Lewis Acid ◽  
Acid Sites ◽  
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

Incorporation of Aluminum and Iron Into the ZSM-12 Zeolite: Synthesis and Characterization of Acid Sites

2002 ◽  
Vol 67 (12) ◽  
pp. 1760-1778 ◽  
Author(s):  
Gabriela Košová ◽  
Jiří Čejka
Keyword(s):  
Lewis Acid ◽  
Crystallization Rate ◽  
Acid Sites ◽  
Sodium Ion ◽  
Synthesis And Characterization ◽  
Lewis Acid Sites ◽  
Structure Directing Agent ◽  
Trivalent Cations ◽  
Brønsted And Lewis Acid

Zeolite ZSM-12 with aluminum and iron in the framework was synthesized in a broad range of Si/Al (Si/Fe) ratios using triethylmethylammonium bromide as structure-directing agent with the aim to characterize the type and concentration of acid sites in dependence on the Si/Al (Si/Fe) ratio and calcination procedure. It was shown that the minimum Si/Al ratio achieved for (Al)ZSM-12 is around 35, which is very close to the minimum Si/Fe ratio ca 37 for (Fe)ZSM-12. The rate of crystallization of (Al)ZSM-12 and (Fe)ZSM-12 depends on the concentration of Al and Fe in the reaction mixture. The higher was the concentration of these trivalent cations, the slower was the apparent crystallization rate. It is suggested that the crystallization rate is controlled by the number of nucleation centers, which depends on the amount of trivalent cations (Al, Fe) in the reaction mixture. Zeolites (Al)ZSM-12 and (Fe)ZSM-12 were calcined under a variety of carefully controlled conditions to investigate the resulting concentration of Brønsted and Lewis acid sites. FTIR spectroscopy used to study the adsorption of acetonitrile-d3 and pyridine on Brønsted and Lewis acid sites revealed that both sites are present in significant concentrations in all calcined (Al)ZSM-12 and (Fe)ZSM-12 zeolites. The highest concentrations of Brønsted sites especially at low Si/Al or Si/Fe ratios were achieved via calcination of the zeolites in a stream of ammonia followed by a repeated sodium ion exchange and further calcination in a stream of air.

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