scholarly journals Effect of Mg/Al2O3 and Calcination Temperature on the Catalytic Decomposition of HFC-134a

Catalysts ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 270 ◽  
Author(s):  
Caroline Andrew Swamidoss ◽  
Mahshab Sheraz ◽  
Ali Anus ◽  
Sangjae Jeong ◽  
Young-Kwon Park ◽  
...  
Keyword(s):  
Surface Area ◽  
Calcination Temperature ◽  
Flow Reactor ◽  
Coke Formation ◽  
Plug Flow ◽  
Strong Acid ◽  
Acid Sites ◽  
Gas Chromatography Mass Spectrometry ◽  
Hfc 134A ◽  
Strong Acid Sites

This paper evaluated the effect of calcination temperature and the use of Mg/Al2O3 on the decomposition of HFC-134a. Two commercialized catalysts, Al2O3 and Mg/Al2O3, were calcined at two different temperatures (500 and 650 °C) and their physicochemical characteristics were examined by X-ray diffraction, Brunauer–Emmett–Teller analysis, and the temperature-programed desorption of ammonia and carbon dioxide analysis. The results show that, in comparison to Al2O3, 5% Mg/Al2O3 exhibited a larger Brunauer–Emmett–Teller surface area and higher acidity. The relative amount of strong acid sites of the catalysts decreased with increasing calcination temperature. Although a more than 90% decomposition rate of HFC-134a was achieved over all catalysts during the sequential decomposition test of HFC-134a using a vertical plug flow reactor connected directly to a gas chromatography/mass spectrometry system, the lifetime of the catalyst differed according to the catalyst type. Compared to Al2O3, Mg/Al2O3 revealed a longer lifetime and less coke formation due to the increased Brunauer–Emmett–Teller surface area and weak Lewis acid sites and basic sites arising from Mg impregnation. Higher temperature calcination extended the catalyst lifetime with the formation of less coke due to the smaller number of strong acid sites, which can lead to severe coke formation. A valuable by-product, trifluoroethylene, was formed as a result of the decomposition. Based on the experimental results, a reaction is proposed which reasonably explains the decomposition reaction.

scholarly journals Effect of the Ni/Al Ratio on the Performance of NiAl2O4 Spinel-Based Catalysts for Supercritical Methylcyclohexane Catalytic Cracking

Catalysts ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 323
Author(s):  
Kyoung Ho Song ◽  
Soon Kwan Jeong ◽  
Byung Hun Jeong ◽  
Kwan-Young Lee ◽  
Hak Joo Kim
Keyword(s):  
Spinel Structure ◽  
Coke Formation ◽  
Strong Acid ◽  
Acid Sites ◽  
The Other ◽  
X Ray ◽  
Temperature Programmed Oxidation ◽  
Temperature Programmed ◽  
Co Precipitation ◽  
Strong Acid Sites

Supercritical methylcyclohexane cracking of NiAl2O4 spinel-based catalysts with varying Ni/Al deficiencies was investigated. Thus, catalysts with Ni content of 10–50 wt.% were prepared by typical co-precipitation methods. The calcined, reduced, and spent catalysts were characterized by X-ray diffraction, O2 temperature-programmed oxidation, NH3 temperature-programmed desorption, N2 physisorption, O2 chemisorption, scanning and transmission electron microscopy, and X-ray fluorescence. The performance and physicochemical properties of the reference stoichiometric Ni3Al7 catalyst differed significantly from those of the other catalysts. Indeed, the Ni-deficient Ni1Al9 catalyst led to the formation of large Ni particles (diameter: 20 nm) and abundant strong acid sites, without spinel structure formation, owing to the excess Al. These acted with sufficient environment and structure to form the coke precursor nickel carbide, resulting in a pressure drop within 17 min. On the other hand, the additional NiO linked to the NiAl2O4 spinel structure of the Al-deficient Ni5Al5 catalyst formed small crystals (10 nm), owing to the excess Ni, and displayed improved Ni dispersion. Thus, dehydrogenation proceeded effectively, thereby improving the resistance to coke formation. This catalytic behavior further demonstrated the remarkable activity and stability of this catalyst under mild conditions (450 °C and 4 Mpa).

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.

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.

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

scholarly journals Synthesis of Uniform Mesoporous Zeolite ZSM-5 Catalyst for Friedel-Crafts Acylation

2019 ◽  
Vol 3 (2) ◽  
pp. 35 ◽  
Author(s):  
Heman Smail ◽  
Mohammad Rehan ◽  
Kafia Shareef ◽  
Zainab Ramli ◽  
Abdul-Sattar Nizami ◽  
...  
Keyword(s):  
Surface Area ◽  
Surface Acidity ◽  
Analytical Techniques ◽  
Acid Sites ◽  
Zeolite Catalysts ◽  
Gas Chromatography Mass Spectrometry ◽  
Crystallographic Structure ◽  
Mesoporous Zeolite ◽  
Mesoporous Zeolites ◽  
Surfactant Templates

This work highlights how the treatment of ZSM-5 (parent Zeolite Socony Mobil–5, Si/Al = 23) with different surfactant templates and alkaline solution, improved the catalytic performance in the Friedel-Crafts acylation of anisole with a propionic anhydride to obtain p-methoxypropiophenone. The modified microporous to mesoporous zeolite catalysts were characterized using different analytical techniques, including X-ray diffraction (XRD), nitrogen porosimetry, Fourier-transform infrared spectroscopy (FT-IR), temperature-programmed desorption (ammonia-TPD) and field emission scanning electron microscopy (FE-SEM) to analyze the crystallographic structure, surface acidity, surface area, porosity, morphology, and particle size. The results showed that the formed mesoporous zeolite by NaOH solution had smaller mesopores (ca. 3.7 nm) as compared to the mesoporous zeolites obtained by surfactant templates, such as, CTAB (ca. 14.9 nm), TPAOH (ca. 11.1 nm) and mixture of CTAB/TPAOH (ca. 15.2 nm). The catalytic acylation reaction was conducted in a batch glass reactor at various temperatures and the products were analyzed using off-line gas chromatography–mass spectrometry (GC-MS). It was found that the activity of treated ZSM-5 with mixed surfactant templates (CTAB/TPAOH) exhibited enhanced selectivity towards the main product (p-methoxypropiophenone) by a factor 1.7 or higher than unmodified ZSM-5 due to its increased surface area by 1.5 times and enhanced acid sites.

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.

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