scholarly journals Mesoporous superacid catalysts for valorisation of refinery naphtha stream

RSC Advances ◽  
2018 ◽  
Vol 8 (59) ◽  
pp. 33702-33709 ◽  
Author(s):  
Sunil Mehla ◽  
Vamsi Krishsna ◽  
Gandham Sriganesh ◽  
Raman Ravishankar
Keyword(s):  
Acid Sites ◽  
Superacid Catalysts

TPA silanol interactions in mesoporous TPA silica composites govern the strength of acid sites, activity and selectivity.

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.

Heteropoly Compounds: Efficient Superacid Catalysts

1994 ◽  
Vol 368 ◽  
Author(s):  
Makoto Misono ◽  
Toshio Okuhara
Keyword(s):  
Acid Catalysis ◽  
Tertiary Structure ◽  
High Surface ◽  
Surface Concentration ◽  
Acid Sites ◽  
Heteropoly Compounds ◽  
Catalytic Activities ◽  
High Surface Concentration ◽  
Superacid Catalysts ◽  
Constituent Elements

ABSTRACTOur recent studies on the acidity and acid catalysis of heteropoly compounds are described, together with a brief introduction of the background. High catalytic activities were observed due to the combination of their superacidity, pseudoliquid behavior, acid-base bifunctionality and/or high surface concentration of proton. It was also shown how the acid strength and the number of acid sites as well as their tertiary structure were controlled by the constituent elements (heteroand addenda-atoms and counter cations), and how those properties were correlated with the catalytic activities

An analytical microscopic study of metals in fluidized catalytic cracking catalyst

1986 ◽  
Vol 44 ◽  
pp. 854-855
Author(s):  
Clifford S. Rainey
Keyword(s):  
Electron Microscopy ◽  
Spatial Distribution ◽  
Catalytic Cracking ◽  
Catalyst Deactivation ◽  
Coke Formation ◽  
Acid Sites ◽  
Y Zeolite ◽  
Fcc Catalyst ◽  
Fluidized Catalytic Cracking ◽  
High Regeneration

The spatial distribution of V and Ni deposited within fluidized catalytic cracking (FCC) catalyst is studied because these metals contribute to catalyst deactivation. Y zeolite in FCC microspheres are high SiO2 aluminosilicates with molecular-sized channels that contain a mixture of lanthanoids. They must withstand high regeneration temperatures and retain acid sites needed for cracking of hydrocarbons, a process essential for efficient gasoline production. Zeolite in combination with V to form vanadates, or less diffusion in the channels due to coke formation, may deactivate catalyst. Other factors such as metal "skins", microsphere sintering, and attrition may also be involved. SEM of FCC fracture surfaces, AEM of Y zeolite, and electron microscopy of this work are developed to better understand and minimize catalyst deactivation.

Probe Reactions Catalyzed by Surface Acid Sites of HTS-1

2010 ◽  
Vol 31 (1) ◽  
pp. 72-77
Author(s):  
Xuanyan LIU ◽  
Dulin YIN ◽  
Huayuan ZHU ◽  
Gang SHEN
Keyword(s):  
Acid Sites

The Effect of Acidity of Al and Fe Silicates with MFI Structure on Benzene and Toluene Alkylation with Isopropyl Alcohol

1996 ◽  
Vol 61 (8) ◽  
pp. 1115-1130 ◽  
Author(s):  
Jiří Čejka ◽  
Naděžda Žilková ◽  
Blanka Wichterlová
Keyword(s):  
Kinetic Study ◽  
Molecular Sieves ◽  
Isopropyl Alcohol ◽  
Acid Sites ◽  
Transport Rate ◽  
Reaction Products ◽  
Oh Groups ◽  
Benzene Alkylation ◽  
Toluene Alkylation ◽  
Low Strength

Kinetic study of toluene and benzene alkylation with isopropyl alcohol on alumo- and ferrisilicates of MFI structure has shown that the alkylation activity does not follow the acidity (both the number and strength of bridging OH groups) of these molecular sieves. The rate of the overall reaction is controlled by the desorption/transport rate of bulky, strongly adsorbed cymenes and cumene. A higher concentration of n-propyltoluenes compared to n-propylbenzene, both undesired reaction products, formed via a bimolecular isomerization of isopropyl aromate with benzene or toluene, was due to the higher reactivity of isopropyltoluene with toluene in comparison with that of cumene with benzene. It is concluded that ferrisilicates of MFI structure possessing low strength acid sites appear to be promising catalysts for achieving both a high isopropyl- and para-selectivity in toluene alkylation to p-cymene.

scholarly journals The C-terminal domain of feline and bovine SAMHD1 proteins has a crucial role in lentiviral restriction

2020 ◽  
Vol 295 (13) ◽  
pp. 4252-4264 ◽  
Author(s):  
Chu Wang ◽  
Kaikai Zhang ◽  
Lina Meng ◽  
Xin Zhang ◽  
Yanan Song ◽  
...  
Keyword(s):  
Proteasomal Degradation ◽  
Acid Sites ◽  
Accessory Protein ◽  
Restriction Profile ◽  
Biological Functions ◽  
Terminal Domain ◽  
Functional Regions ◽  
Viral Restriction ◽  
Primate Lentiviruses

SAM and HD domain-containing protein 1 (SAMHD1) is a host factor that restricts reverse transcription of lentiviruses such as HIV in myeloid cells and resting T cells through its dNTP triphosphohydrolase (dNTPase) activity. Lentiviruses counteract this restriction by expressing the accessory protein Vpx or Vpr, which targets SAMHD1 for proteasomal degradation. SAMHD1 is conserved among mammals, and the feline and bovine SAMHD1 proteins (fSAM and bSAM) restrict lentiviruses by reducing cellular dNTP concentrations. However, the functional regions of fSAM and bSAM that are required for their biological functions are not well-characterized. Here, to establish alternative models to investigate SAMHD1 in vivo, we studied the restriction profile of fSAM and bSAM against different primate lentiviruses. We found that both fSAM and bSAM strongly restrict primate lentiviruses and that Vpx induces the proteasomal degradation of both fSAM and bSAM. Further investigation identified one and five amino acid sites in the C-terminal domain (CTD) of fSAM and bSAM, respectively, that are required for Vpx-mediated degradation. We also found that the CTD of bSAM is directly involved in mediating bSAM's antiviral activity by regulating dNTPase activity, whereas the CTD of fSAM is not. Our results suggest that the CTDs of fSAM and bSAM have important roles in their antiviral functions. These findings advance our understanding of the mechanism of fSAM- and bSAM-mediated viral restriction and might inform strategies for improving HIV animal models.

scholarly journals Plastic waste to fuels by hydrocracking at mild conditions

2021 ◽  
Vol 7 (17) ◽  
pp. eabf8283
Author(s):  
Sibao Liu ◽  
Pavel A. Kots ◽  
Brandon C. Vance ◽  
Andrew Danielson ◽  
Dionisios G. Vlachos
Keyword(s):  
Direct Method ◽  
Acid Sites ◽  
Liquid Fuels ◽  
High Yield ◽  
Tandem Catalysis ◽  
Hy Zeolite ◽  
Environmental Threat ◽  
Single Use ◽  
Initial Activation ◽  
A Direct Method

Single-use plastics impose an enormous environmental threat, but their recycling, especially of polyolefins, has been proven challenging. We report a direct method to selectively convert polyolefins to branched, liquid fuels including diesel, jet, and gasoline-range hydrocarbons, with high yield up to 85% over Pt/WO3/ZrO2 and HY zeolite in hydrogen at temperatures as low as 225°C. The process proceeds via tandem catalysis with initial activation of the polymer primarily over Pt, with subsequent cracking over the acid sites of WO3/ZrO2 and HY zeolite, isomerization over WO3/ZrO2 sites, and hydrogenation of olefin intermediates over Pt. The process can be tuned to convert different common plastic wastes, including low- and high-density polyethylene, polypropylene, polystyrene, everyday polyethylene bottles and bags, and composite plastics to desirable fuels and light lubricants.

Deep Eutectic Solvents with Multiple Weak Acid Sites for Highly Efficient, Reversible and Selective Absorption of Ammonia

2021 ◽  
pp. 118791
Author(s):  
Ning-Ning Cheng ◽  
Zi-Liang Li ◽  
Hong-Chao Lan ◽  
Wen-Long Xu ◽  
Wen-Jing Jiang ◽  
...  
Keyword(s):  
Deep Eutectic Solvents ◽  
Acid Sites ◽  
Weak Acid ◽  
Selective Absorption ◽  
Highly Efficient

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).

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