scholarly journals Ethylene Oligomerization over Nickel Supported Silica-Alumina Catalysts with High Selectivity for C10+ Products

Catalysts ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 180 ◽  
Author(s):  
Lei Chen ◽  
Guangci Li ◽  
Zhong Wang ◽  
Shuangju Li ◽  
Mingjie Zhang ◽  
...  
Keyword(s):  
Reaction Temperature ◽  
Aging Temperature ◽  
Active Sites ◽  
High Selectivity ◽  
Acid Sites ◽  
Ethylene Oligomerization ◽  
Octahedral Coordination ◽  
Activation Temperature ◽  
High Aging Temperature ◽  
Silica Alumina

The nickel (II) loading silica-alumina under various treatments in terms of aging temperature, Si/Al ratio and activation temperature were investigated by XRD, N2 adsorption-desorption, TEM, UV-Vis, NH3-TPD and XRF and then applied to catalyze the ethylene oligomerization. High aging temperature, low Si/Al ratio and high activation temperature were beneficial to high selectivity for C10+ products because of a reasonable match between Ni active sites and acid sites, high Ni loading content and less octahedral coordination Ni2+ species, respectively. Ni loading content was more important than the number of acid sites for high yield of C10+ products, and less octahedral coordination Ni2+ species favored less by-products produced at high reaction temperature. In addition, other experimental conditions, such as reaction temperature, weight hourly space velocity (WHSV) and nickel precursor were discussed in the paper.

Effect of activation temperature on acidity of alumina, silica-alumina and cobalt-molybdenum-alumina catalysts

1985 ◽  
Vol 50 (6) ◽  
pp. 1268-1273 ◽  
Author(s):  
Zdeněk Vít
Keyword(s):  
Acid Sites ◽  
Hydroxyl Groups ◽  
Activation Temperature ◽  
Cumene Cracking ◽  
Surface Hydroxyl ◽  
Catalytic Activities ◽  
Surface Hydroxyl Groups ◽  
Silica Alumina ◽  
Effect Of Surface ◽  
Alumina Catalysts

The effect of surface dehydration on the acidity of silica-alumina and cobalt-molybdenum-alumina catalysts has been studied and compared with alumina. The catalysts were characterized by surface hydroxyl groups concentrations, acid sites concentrations and by catalytic activities in paraldehyde depolymerisation and cumene cracking. It was found that the acidity of alumina and cobalt-molybdenum-alumina catalysts increases significantly with surface dehydration and attains maximum after activation at 500-550 °C. Silica-alumina is strongly acidic even in the hydrated state, the acidity being formed already at relatively low temperature around 100 °C.

Mildly Acidic Aluminosilicate Catalysts for Stable Performance in Ethanol Dehydration

2020 ◽  
Author(s):  
Ales Styskalik ◽  
Vit Vykoukal ◽  
Luca Fusaro ◽  
Carmela Aprile ◽  
Damien Debecker
Keyword(s):  
Sol Gel ◽  
Coke Formation ◽  
Strong Acid ◽  
Acid Sites ◽  
High Specific Surface Area ◽  
Ethylene Oligomerization ◽  
Zeolite Catalysts ◽  
Activity Levels ◽  
Ethanol Dehydration ◽  
Silica Alumina

Ethanol dehydration is effectively catalyzed by strongly acidic zeolite catalysts which are known, however, to exhibit poor time on stream stability. Alumina and silica-alumina on the other hand are relatively stable but reach only low activity levels. Here, a series of aluminosilicate catalysts (Si:Al ratio = 16) was prepared by non-hydrolytic sol-gel (NHSG) and are shown to feature an intermediate level of activity, between the HZSM-5 zeolite and a commercial silica-alumina. Importantly, the best samples, were very stable with time on stream. Unlike HZSM-5, which also catalyzes ethylene oligomerization due to its strong acid sites and is therefore prone to coking, NHSG prepared catalysts did not produce any traces of ethylene oligomers and did not show any trace of coke formation. Characterization (ICP-OES, N<sub>2</sub> physisorption, TEM, XPS, IR coupled with pyridine adsorption, Raman spectroscopy, solid state NMR spectroscopy) reveal that the unconventional synthetic method presented here allowed to prepare mesoporous aluminosilicate materials with a remarkable degree of homogeneity. It is this thorough dispersion of Al in the amorphous silicate matrix which is responsible for the formation of acid sites which are intermediate (in terms of strength and nature) between those of commercial silica-alumina and HZSM-5 zeolite. The texture of the best NHSG catalyst – mainly mesoporous with a high specific surface area (800 m² g<sup>−1</sup>) and pore volume (0.5 cm³ g<sup>−1</sup>) – was also unaffected after reaction. To overcome deactivation issues in ethanol dehydration, this study suggests to target amorphous aluminosilicate catalysts with open mesoporosity and with an intimate mixing of Al and Si.

Unraveling the real active sites of an amorphous silica–alumina-supported nickel catalyst for highly efficient ethylene oligomerization

2021 ◽  
Author(s):  
Jinghua Xu ◽  
Ruifeng Wang ◽  
Lirong Zheng ◽  
Junguo Ma ◽  
Wenjun Yan ◽  
...  
Keyword(s):  
Nickel Catalyst ◽  
Amorphous Silica ◽  
Active Sites ◽  
Ethylene Oligomerization ◽  
Supported Nickel Catalyst ◽  
The Real ◽  
Highly Efficient ◽  
Silica Alumina

The Ni+ species in a heterogeneous N2-pretreated amorphous silica–alumina-supported nickel catalyst acted as the active sites for ethylene oligomerization.

Mildly Acidic Aluminosilicate Catalysts for Stable Performance in Ethanol Dehydration

2020 ◽  
Author(s):  
Ales Styskalik ◽  
Vit Vykoukal ◽  
Luca Fusaro ◽  
Carmela Aprile ◽  
Damien Debecker
Keyword(s):  
Sol Gel ◽  
Coke Formation ◽  
Strong Acid ◽  
Acid Sites ◽  
High Specific Surface Area ◽  
Ethylene Oligomerization ◽  
Zeolite Catalysts ◽  
Activity Levels ◽  
Ethanol Dehydration ◽  
Silica Alumina

Ethanol dehydration is effectively catalyzed by strongly acidic zeolite catalysts which are known, however, to exhibit poor time on stream stability. Alumina and silica-alumina on the other hand are relatively stable but reach only low activity levels. Here, a series of aluminosilicate catalysts (Si:Al ratio = 16) was prepared by non-hydrolytic sol-gel (NHSG) and are shown to feature an intermediate level of activity, between the HZSM-5 zeolite and a commercial silica-alumina. Importantly, the best samples, were very stable with time on stream. Unlike HZSM-5, which also catalyzes ethylene oligomerization due to its strong acid sites and is therefore prone to coking, NHSG prepared catalysts did not produce any traces of ethylene oligomers and did not show any trace of coke formation. Characterization (ICP-OES, N<sub>2</sub> physisorption, TEM, XPS, IR coupled with pyridine adsorption, Raman spectroscopy, solid state NMR spectroscopy) reveal that the unconventional synthetic method presented here allowed to prepare mesoporous aluminosilicate materials with a remarkable degree of homogeneity. It is this thorough dispersion of Al in the amorphous silicate matrix which is responsible for the formation of acid sites which are intermediate (in terms of strength and nature) between those of commercial silica-alumina and HZSM-5 zeolite. The texture of the best NHSG catalyst – mainly mesoporous with a high specific surface area (800 m² g<sup>−1</sup>) and pore volume (0.5 cm³ g<sup>−1</sup>) – was also unaffected after reaction. To overcome deactivation issues in ethanol dehydration, this study suggests to target amorphous aluminosilicate catalysts with open mesoporosity and with an intimate mixing of Al and Si.

scholarly journals H2O and/or SO2 Tolerance of Cu-Mn/SAPO-34 Catalyst for NO Reduction with NH3 at Low Temperature

Catalysts ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 289 ◽  
Author(s):  
Guofu Liu ◽  
Wenjie Zhang ◽  
Pengfei He ◽  
Shipian Guan ◽  
Bing Yuan ◽  
...  
Keyword(s):  
Low Temperature ◽  
Reaction Temperature ◽  
Active Sites ◽  
Competitive Adsorption ◽  
Catalytic Reduction ◽  
Acid Sites ◽  
Impregnation Method ◽  
Spent Catalyst ◽  
Poisoning Effect ◽  
Negative Effect

A series of molecular sieve catalysts (Cu–Mn/SAPO-34) with different loadings of Cu and Mn components were prepared by the impregnation method. The deNOx activity of the catalyst was investigated during the selective catalytic reduction (SCR) of NO with NH3 in the temperature range of 120 °C to 330 °C, including the effects of H2O vapors and SO2. In order to understand the poisoning mechanism by the injection of H2O and/or SO2 into the feeding gas, the characteristics of the fresh and spent catalyst were identified by means of Brunner−Emmet−Teller (BET), X-ray Diffraction (XRD), Scanning Electronic Microscopy (SEM) and Thermal Gravity- Differential Thermal Gravity (TG-DTG). The conversion of NO by the catalyst can achieve at 72% under the reaction temperature of 120 °C, while the value reached more than 90% under the temperature between 180 °C and 330 °C. The deNOx activity test shows that the H2O has a reversible negative effect on NO conversion, which is mainly due to the competitive adsorption of H2O and NH3 on Lewis acid sites. When the reaction temperature increases to 300 °C, the poisoning effect of H2O can be negligible. The poisoning effect of SO2 on deNOx activity is dependent on the reaction temperature. At low temperature, the poisoning effect of SO2 is permanent with no recovery of deNOx activity after the elimination of SO2. The formation of (NH4)2SO4, which results in the plug of active sites and a decrease of surface area, and the competitive adsorption of SO2 and NO should be responsible for the loss of deNOx activity over Cu/SAPO-34.

scholarly journals Zeolite Catalyzed Aldol Condensation Reactions

2015 ◽  
Vol 3 (1) ◽  
pp. 1-8
Author(s):  
Adedayo I. Inegbenebor ◽  
Raphael C. Mordi ◽  
Oluwakayode M. Ogunwole
Keyword(s):  
Lewis Acids ◽  
Active Sites ◽  
Aldol Condensation ◽  
Condensation Product ◽  
Acid Sites ◽  
Weak Acid ◽  
Aldol Reactions ◽  
Condensation Reactions ◽  
Silica Alumina ◽  
Aldol Condensation Reactions

The review is based on the description of zeolite structure, uses, synthesis, and catalytic aldol reaction in aldol condensation. An internal aldolcondensation reaction has been achieved over ZSM-5 zeolite with high silica-alumina ratio at 350oC. It therefore follows that zeolite canfunction as a catalyst in aldol type condensation reactions and that weak acid sites as well as a small number of active sites favor the aldolcondensation reaction of carbonyl compounds. However, the mixed condensation product was found to be favored at temperatures above 300oCand the self-condensation of ethanal to crotonaldehyde was favored at temperatures below 300oC. It has also been suggested that both Brønstedand Lewis acids are involved in aldol reactions with Lewis acid sites the most probable catalytic sites. The zeolite group of minerals has founduse in many chemical and allied industries.DOI: http://dx.doi.org/10.3126/ijasbt.v3i1.12291  Int J Appl Sci Biotechnol, Vol. 3(1): 1-8 

scholarly journals On the Role of Protonic Acid Sites in Cu Loaded FAU31 Zeolite as a Catalyst for the Catalytic Transformation of Furfural to Furan

Molecules ◽  
2021 ◽  
Vol 26 (7) ◽  
pp. 2015
Author(s):  
Łukasz Kuterasiński ◽  
Małgorzata Smoliło-Utrata ◽  
Joanna Kaim ◽  
Wojciech Rojek ◽  
Jerzy Podobiński ◽  
...  
Keyword(s):  
Active Sites ◽  
Acid Sites ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Brønsted Acid Sites ◽  
Protonic Acid ◽  
Brönsted Acid ◽  
Brönsted Acid Sites ◽  
Bronsted Acid Sites

The aim of the present paper is to study the speciation and the role of different active site types (copper species and Brønsted acid sites) in the direct synthesis of furan from furfural catalyzed by copper-exchanged FAU31 zeolite. Four series of samples were prepared by using different conditions of post-synthesis treatment, which exhibit none, one or two types of active sites. The catalysts were characterized by XRD, low-temperature sorption of nitrogen, SEM, H2-TPR, NMR and by means of IR spectroscopy with ammonia and CO sorption as probe molecules to assess the types of active sites. All catalyst underwent catalytic tests. The performed experiments allowed to propose the relation between the kind of active centers (Cu or Brønsted acid sites) and the type of detected products (2-metylfuran and furan) obtained in the studied reaction. It was found that the production of 2-methylfuran (in trace amounts) is determined by the presence of the redox-type centers, while the protonic acid sites are mainly responsible for the furan production and catalytic activity in the whole temperature range. All studied catalysts revealed very high susceptibility to coking due to polymerization of furfural.

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