Generation and Identification of Strong Acid Sites in AlMCM-41 Prepared by Gel Equilibrium Adjustment Method

1997 ◽  
Vol 26 (7) ◽  
pp. 637-638 ◽  
Author(s):  
K. Ramesh Reddy ◽  
Nobuyuki Araki ◽  
Miki Niwa
Keyword(s):  
Strong Acid ◽  
Acid Sites ◽  
Adjustment Method ◽  
Strong Acid Sites

Reaction Mechanism for CCl2F2 Catalytic Decomposition over MoO3/ZrO2

2013 ◽  
Vol 295-298 ◽  
pp. 326-330 ◽  
Author(s):  
Tian Cheng Liu ◽  
Yu Jiao Guo ◽  
Ping Ning ◽  
Ming Long Yuan
Keyword(s):  
Reaction Mechanism ◽  
Main Product ◽  
Solid Acid ◽  
Fixed Bed ◽  
Catalytic Decomposition ◽  
Strong Acid ◽  
Acid Sites ◽  
Fixed Bed Reactor ◽  
Surface Intermediate ◽  
Strong Acid Sites

Catalytic hydrolysis decomposition of dichlorodifluoromethane (CCl2F2) in the presence of water vapor and oxygen was studied over a series of solid acids using a fixed-bed reactor. Solid acid MoO3/ZrO2 displayed the highest activity, over which the conversion of CCl2F2 reached 100 % at 250 °C. CO2 was the main-product and the selectivity to CClF3 remained lower than 28.0 %. CO was not detected as by-product. The decomposition activity depended on the calcination temperature and the ZrO2 content. The activity of solid acid MoO3/ZrO2 correlates well with its specific surface area and the amount of medium-strong acid sites on the surface. To explain the reaction mechanism for CCl2F2 catalytic decomposition over MoO3/ZrO2, a surface intermediate, Osurface-CF2-Osurface is proposed.

scholarly journals Controlled direct synthesis of single- to multiple-layer MWW zeolite

2020 ◽  
Author(s):  
Jie-Qiong Chen ◽  
Yu-Zhao Li ◽  
Qing-Qing Hao ◽  
Huiyong Chen ◽  
Zhao-Tie Liu ◽  
...  
Keyword(s):  
Large Scale ◽  
Direct Synthesis ◽  
Single Layer ◽  
Strong Acid ◽  
Acid Sites ◽  
Synthesis Conditions ◽  
Alkylation Of Benzene ◽  
Controlled Structure ◽  
Strong Acid Sites ◽  
Mww Zeolite

ABSTRACT The minimized diffusion limitation and completely exposed strong acid sites of the ultrathin zeolites make it an industrially important catalyst especially for converting bulky molecules. However, the structure-controlled and large-scale synthesis of the material is still a challenge. In this work, the direct synthesis of the single-layer MWW zeolite was demonstrated by using hexamethyleneimine and amphiphilic organosilane as structure-directing agents. Characterization results confirmed the formation of the single-layer MWW zeolite with high crystallinity and excellent thermal/hydrothermal stability. The formation mechanism was rigorously revealed as the balanced rates between the nucleation/growth of the MWW nanocrystals and the incorporation of the organosilane into the MWW unit cell, which is further supported by the formation of MWW nanosheets with tunable thickness via simply changing synthesis conditions. The commercially available reagents, well-controlled structure and the high catalytic stability for the alkylation of benzene with 1-dodecene make it an industrially important catalyst.

scholarly journals Effect of support acidity during selective hydrogenolysis of glycerol over supported palladium–ruthenium catalysts

2020 ◽  
Vol 378 (2176) ◽  
pp. 20200055
Author(s):  
Susana Guadix-Montero ◽  
Alba Santos-Hernandez ◽  
Andrea Folli ◽  
Meenakshisundaram Sankar
Keyword(s):  
Catalytic Activity ◽  
Supported Catalysts ◽  
Bond Cleavage ◽  
Strong Acid ◽  
Acid Sites ◽  
Ruthenium Catalysts ◽  
Impregnation Method ◽  
Selective Hydrogenolysis ◽  
Strong Acid Sites ◽  
Effect Of Support

We report the role of the acidity of support during the selectivity hydrogenolysis of glycerol over supported bimetallic palladium–ruthenium (PdRu) catalysts. The PdRu nanoparticles were supported on a series of metal oxides and zeolitic supports via the modified impregnation method and tested for the liquid-phase hydrogenolysis of glycerol using gaseous hydrogen. The relative acid site densities of selected catalysts were determined by ammonia temperature-programmed desorption and pyridine desorption experiments. Based on these studies, we report a direct correlation between the catalytic activity (conversion and 1,2 propane diol yield) and two different acid sites (strong acid sites and very strong acid sites). Besides zeolite-supported catalysts, TiO 2 supported PdRu nanoparticles exhibit moderate catalytic activity; however, this catalyst shows high selectivity for the desired C–O bond cleavage to produce C3 products over the undesired C–C bond cleavage to produce < C3 products. This article is part of a discussion meeting issue ‘Science to enable the circular economy’.

Reaction Characteristic of MeAPSO-34 (Me=Mn, Co) Catalysts for Olefins Production from Dimethyl Ether

2012 ◽  
Vol 550-553 ◽  
pp. 416-419
Author(s):  
Young Ho Kim ◽  
Su Gyung Lee ◽  
Eun Jee Kang ◽  
Hyo Sub Kim ◽  
Chu Sik Park
Keyword(s):  
Dimethyl Ether ◽  
Strong Acid ◽  
Acid Sites ◽  
Coke Deposition ◽  
Light Olefins ◽  
Co Catalysts ◽  
Strong Acid Sites ◽  
Reaction Characteristic ◽  
Catalyst Lifetime

In DME to olefins (DTO) reaction, SAPO-34 catalyst with CHA structure is well known to be one of the catalysts with good performance. However, the SAPO-34 catalyst is easily deactivated due to coke deposition during DTO reaction. In this study, MeAPSO-34 catalysts (Me=Mn, Co) were prepared for the increase of the catalyst lifetime and their properties have been characterized by XRD and SEM. The DTO reaction was carried out over the MeAPSO-34 catalysts, and the results were compared with the SAPO-34 catalyst. The lifetime of MeAPSO-34 catalysts with high DME conversion and selectivity of light olefins was prolonged than that of the SAPO-34 catalyst. It may be concluded that the decrease of strong acid sites, which were responsible for the formation of coke, affect on the lifetime of the MeAPSO-34 catalysts. In addition, the CoAPSO-34 catalyst with a Co additive showed the best performance in terms of the catalytic lifetime and the selectivity to light olefins.

Effect of autotransformation on the layer charge of smectites determined by the alkylammonium method

Clay Minerals ◽  
1997 ◽  
Vol 32 (4) ◽  
pp. 623-632 ◽  
Author(s):  
M. Janek ◽  
P. Komadel ◽  
G. Lagaly
Keyword(s):  
Aqueous Dispersion ◽  
Strong Acid ◽  
Acid Sites ◽  
Weak Acid ◽  
Layer Charge ◽  
Exchange Method ◽  
Density Distributions ◽  
Titration Curves ◽  
The Mean ◽  
Strong Acid Sites

AbstractHydrogen-forms of <2 µm fractions of six bentonites of various Fe contents were prepared by H+→OH-→H+ ion exchange using resins. Potentiometric titration curves revealed that the number of strong acid sites varied and accounted for 60-95% of the total acidity in the freshly prepared H-forms. The number of strong acid sites decreased and that of the weak acid sites increased on ageing. The process of autotransformation in aqueous dispersion at 90~ was completed within four days. Layer-charge distributions of all samples were inhomogeneous with layer charges from 0.25-0.39 Eq/unit O10(OH)2. Oxalate pretreatment of the samples resulted in changes in the layer-charge distribution due to the removal of readily soluble phases which may have blocked exchange sites. After autotransformation, the alkylammonium exchange method revealed inhomogeneous charge density distributions; the fraction of layers of the highest charge decreased. Comparison of total CEC obtained from potentiometric curves and interlamellar CEC calculated from the mean layer charge confirmed attack of protons from particle edges. However, for several samples the structural attack may also occur from the interlayer space. Autotransformation of the Hsmectites decreased the mean layer charge. Protons probably attack the Mg(O,OH)6 octahedra preferentially during the autotransformation.

scholarly journals Catalytic Rapid Pyrolysis ofQuercus variabilisover Nanoporous Catalysts

2015 ◽  
Vol 2015 ◽  
pp. 1-6 ◽  
Author(s):  
Hyeon Koo Kang ◽  
In-Gu Lee ◽  
Kyong-Hwan Lee ◽  
Beom-Sik Kim ◽  
Tae Su Jo ◽  
...  
Keyword(s):  
Oil Quality ◽  
Strong Acid ◽  
Abundant Species ◽  
Acid Sites ◽  
Weak Acid ◽  
Nanoporous Materials ◽  
Bio Oil ◽  
Strong Acid Sites ◽  
Rapid Pyrolysis ◽  
Mcm 41

Catalytic rapid pyrolysis ofQuercus variabilis, a Korean native tree species, was carried out using Py-GC/MS. Mesoporous MFI, which has both nanopores and micropores, and three nanoporous materials, Al-MCM-41, Al-SBA-15, andγ-Al2O3, were used as the catalyst. The acid sites of mesoporous MFI were strong Brønsted acid sites, whereas those of nanoporous materials were mostly weak acid sites. The composition of the product bio-oil varied greatly depending on the acid characteristics of the catalyst used. Phenolics were the most abundant species in the bio-oil, followed by acids and furanics, obtained over Al-MCM-41 or Al-SBA-15 with weak acid sites, whereas aromatics were the most abundant species produced over mesoporous MFI with strong acid sites, followed by phenolics. Aromatics, phenolics, and furanics are all important chemicals contributing to the improvement of bio-oil quality.

scholarly journals Enhancing Methane Conversion by Modification of Zn States in Co-Reaction of MTA

Catalysts ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1540
Author(s):  
Yue Yu ◽  
Zhixiang Xi ◽  
Bingjie Zhou ◽  
Binbo Jiang ◽  
Zuwei Liao ◽  
...  
Keyword(s):  
Active Site ◽  
Methane Conversion ◽  
Strong Acid ◽  
Acid Sites ◽  
Methane Activation ◽  
Reaction Conditions ◽  
Holy Grail ◽  
Highly Efficient ◽  
Strong Acid Sites ◽  
Capacity Loading

Limited by harsh reaction conditions, the activation and utilization of methane were regarded as holy grail reaction. Co-reaction with methanol, successfully realizing mild conversion below 450 °C, provides practical strategies for methane conversion on metal-loaded ZSM-5 zeolites, especially for highly efficient Zn loaded ones. However, Zn species, regarded as active acid sites on the zeolite, have not been sufficiently studied. In this paper, Zn-loaded ZSM-5 zeolite was prepared, and Zn was modified by capacity, loading strategy, and treating atmosphere. Apparent methane conversion achieves 15.3% for 1.0Zn/Z-H2 (16.8% as calculated net conversion) with a significantly reduced loading of 1.0 wt.% against deactivation, which is among the best within related zeolite materials. Besides, compared to the MTA reaction, the addition of methane promotes the high-valued aromatic production from 49.4% to 54.8%, and inhibits the C10+ production from 7.8% to 3.6%. Notably, Zn2+ is found to be another active site different from the reported ZnOH+. Medium strong acid sites are proved to be beneficial for methane activation. This work provides suggestions for the modification of the Zn active site, in order to prepare highly efficient catalysts for methane activation and BTX production in co-reaction with methanol.

scholarly journals Optimized Pore Structures of Hierarchical HY Zeolites for Highly Selective Production of Methyl Methoxyacetate

Catalysts ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 865 ◽  
Author(s):  
Fei Chen ◽  
Dongxi Zhang ◽  
Lei Shi ◽  
Yan Wang ◽  
Guangwen Xu
Keyword(s):  
Strong Acid ◽  
Treatment Method ◽  
Alkaline Treatment ◽  
Acid Sites ◽  
Relative Crystallinity ◽  
Mesoporous Zeolites ◽  
Pore Structures ◽  
The Stability ◽  
Strong Acid Sites ◽  
Hy Zeolites

Several organic templates were introduced during acid or alkaline treatment to optimize pore structures of hierarchical HY zeolites. The influences of category and concentration of templates on the pore structures and acidity of hierarchical HY zeolites were systemically studied. The N2 adsorption-desorption showed that the micropore amount of the optimized HY zeolites obviously increased, while both the large mesopore size and amount remained almost unchanged. The XRD and NH3-TPD revealed that the optimized HY zeolites exhibited higher relative crystallinity and medium-strong acid sites amount than those of hierarchical HY zeolites produced without the addition of templates. The optimized HY zeolites were used for the synthesis of methyl methoxyacetate (MMAc) from dimethoxymethane (DMM) carbonylation. In comparison with parent HY, the conversion and the selectivity clearly increased from 36.43% to 96.32% and from 11.06% to 92.35%, respectively. The stability of the optimized zeolite was also conducted under the same conditions. The conversion and the selectivity remained nearly unchanged even through 24 h reaction, showing that the performance was extremely stable. The TG-DTA and GC-MS also indicated that the generation of coke was effectively inhibited. This catalyst treatment method, which is facile and highly efficient, provided a route for producing mesoporous zeolites.

scholarly journals Synthesis of micro–mesoporous ZSM-5 zeolite with microcrystalline cellulose as co-template and catalytic cracking of polyolefin plastics

RSC Advances ◽  
2020 ◽  
Vol 10 (37) ◽  
pp. 22126-22136
Author(s):  
Hongchang Yu ◽  
Fuwei Li ◽  
Wen He ◽  
Caifeng Song ◽  
Yansong Zhang ◽  
...  
Keyword(s):  
Microcrystalline Cellulose ◽  
Catalytic Cracking ◽  
Strong Acid ◽  
Acid Sites ◽  
Strong Acid Sites

Microcrystalline cellulose as co-template enhances the formation of mesopores and strong acid sites in ZSM-5 zeolites.

Coke on Zn/Hβ Catalyst in Ethanol to Propylene

2014 ◽  
Vol 962-965 ◽  
pp. 719-722
Author(s):  
Wen Ting Qu ◽  
Ting Bai ◽  
Feng Wang ◽  
Xi Ling Liu ◽  
Xin Zhang
Keyword(s):  
Physicochemical Properties ◽  
Continuous Flow ◽  
External Surface ◽  
Fixed Bed ◽  
Strong Acid ◽  
Acid Sites ◽  
Fixed Bed Reactor ◽  
Isothermal Adsorption ◽  
Strong Acid Sites ◽  
Adsorption Desorption

Coke on Zn/Hβ catalyst in ethanol to propylene was studied in continuous-flow fixed-bed reactor. The physicochemical properties of these fresh and used catalysts were characterized by NH3-TPD, N2 isothermal adsorption-desorption and TPO. These results showed that the medium and strong acid sites might be responsible for the production of coke and coke mainly deposited on external surface and microporous mouth. In addition, the coke might be consisted of soft coke and hard coke.

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