scholarly journals The ZSM-5-Catalyzed Oxidation of Benzene to Phenol with N2O: Effect of Lewis Acid Sites

Catalysts ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 44
Author(s):  
Cui Ouyang ◽  
Yingxia Li ◽  
Jianwei Li
Keyword(s):  
Active Sites ◽  
Acid Sites ◽  
X Ray Diffraction ◽  
Remarkable Feature ◽  
Chemisorbed Oxygen ◽  
Lewis Acidic Sites ◽  
Acidic Sites ◽  
Adsorption Desorption ◽  
Oxidation Of Benzene ◽  
N2o Selectivity

The oxidation of benzene to phenol (BTOP) with N2O as the oxidant has been studied with a variety of Fe/ZSM-5 catalysts. The literature has conclusively proven that Fe2+ sites are the active sites. However, some studies have suggested that the Lewis acidic sites (LAS) are responsible for the generation of the active chemisorbed oxygen. Nevertheless, there is no clear relationship between the LAS and the N2O selectivity to phenol. In an effort to elucidate the effects of LAS on BTOP with various ZSM-5 catalysts, we investigated the initial N2O selectivity to phenol. Here we show that the initial N2O selectivity to phenol is negative with the amount of LAS over a certain range. The catalyst H-ZSM-5-ST (H-ZSM-5 treated with water vapor) showed a remarkable initial N2O selectivity to phenol as high as 95.9% with a 0.021 mmol g−1 LAS concentration on the surface of the catalyst, while the Fe/ZSM-5 catalyst demonstrated the lowest initial N2O selectivity to phenol (11.7%) with the highest LAS concentration (0.137 mmol g−1). Another remarkable feature is that steaming was more effective than Fe ion exchange and high temperature calcining. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), N2-adsorption-desorption, UV-vis, NH3-TPD and pyridine Fourier transform infrared (FT-IR) techniques. Our results demonstrate how the concentration of LAS is likely to affect the initial N2O selectivity to phenol within a certain range (0.021–0.137 mmol g−1). This research has demonstrated the synergy between the active Fe2+ sites and LAS.

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).

Dehydration of lactic acid to acrylic acid over lanthanum phosphate catalysts: the role of Lewis acid sites

2016 ◽  
Vol 18 (34) ◽  
pp. 23746-23754 ◽  
Author(s):  
Zhen Guo ◽  
De Sheng Theng ◽  
Karen Yuanting Tang ◽  
Lili Zhang ◽  
Lin Huang ◽  
...  
Keyword(s):  
Lactic Acid ◽  
Acrylic Acid ◽  
Lewis Acid ◽  
Acid Sites ◽  
Lewis Acid Sites ◽  
Lanthanum Phosphate ◽  
Lewis Acidic Sites ◽  
Acidic Sites ◽  
Nano Rods

Lewis acidic sites on the surface of lanthanum phosphate nano-rods play a crucial role on the catalytic dehydration of lactic acid to acrylic acid.

The Application of Mesoporous ZSM-5 Zeolite in the ULSD Catalysts

2020 ◽  
Vol 4 (4) ◽  
pp. 1-3
Author(s):  
Liu L
Keyword(s):  
Catalytic Performance ◽  
Nitrogen Compounds ◽  
In Situ Ftir ◽  
X Ray Diffraction ◽  
N2 Adsorption ◽  
X Ray ◽  
Acidic Sites ◽  
Adsorption Desorption ◽  
Al2o3 Catalyst

The mesoporous ZSM-5 zeolite containing MoCoP/Al2O3 catalyst (C12-ZSM5) with the mixture of Al2O3 and mesoporous ZSM- 5 zeolite as carrier was synthesized. The catalytic performance of C12-ZSM5 catalyst was evaluated by the hydrodesulfurization (HDS) of different diesel feedstock. The carriers and catalysts were characterized by N2 adsorption-desorption, pyridine-FTIR, X-ray diffraction (XRD) and CO in-situ FTIR (CO-FTIR) techniques. Results showed that mesoporous ZSM-5 can improve the acidity of the catalyst and increase the number of MoCoS active phases. The C12-ZSM5 catalyst had low HDS and HDN activity, because the acidic sites of mesoporous ZSM-5 were easily occupied by nitrogen compounds. The HDS activity of C12-ZSM5 catalyst was fully exploited by using graded packing technology, the sulfur content of product oil was 5.9 ng/μL. The relative HDS activity of C12-ZSM5 catalyst is 1.47 times that of FHUDS-8 catalyst.

Synthesis, Physicochemical Properties and Catalytic Performance of a Modified ZSM-5 Molecular Sieve

2011 ◽  
Vol 197-198 ◽  
pp. 1042-1046
Author(s):  
Wei Qiao Liu ◽  
Gong Li ◽  
Hui Juan Tong ◽  
Wei Ning Lei ◽  
Tong Ming Shang ◽  
...  
Keyword(s):  
Molecular Sieve ◽  
Catalytic Performance ◽  
Mesoporous Molecular Sieve ◽  
Acid Sites ◽  
X Ray Diffraction ◽  
Alkyl Benzene ◽  
Carbon Template ◽  
Conventional Process ◽  
Alkylation Of Benzene ◽  
Adsorption Desorption

A modified ZSM-5 molecular sieve was prepared by the combination of recrystallization and carbon template methods. The samples were characterized by X-ray diffraction, N2 adsorption-desorption, NH3-TPD, TEM and SEM. The results show that the modified ZSM-5 molecular sieve has double pore distribution. The diameters of the two kinds of channels are 0.51~0.56 nm and 1.4~1.6 nm, respectively. In addition, the modified HZSM-5 (H-type ZSM-5) sample mainly has moderate strength of acid sites. Finally, the alkylation of benzene with 1-dodecene olefin was used to evaluate the catalytic performance of the as-synthesized modified ZSM-5 on macromolecules. The conversions of 1-dodecene on the modified ZSM-5, ZSM-5 prepared by conventional process and aluminum-containing SBA-15 mesoporous molecular sieve are 96%, 39% and 83%, respectively. And the selectivities of long chain alkyl benzene on those are 97%, 68% and 91%, respectively. The catalytic properties of the modified ZSM-5 on macromolecules are superior to those of ZSM-5 prepared by conventional process and aluminum-containing SBA-15 mesoporous molecular sieve.

Plasma-Treated Ce/TiO2-Palygorskite Catalyst for the NH3-SCR of NOx

2019 ◽  
Vol 41 (1) ◽  
pp. 90-90
Author(s):  
Kaige Chen Kaige Chen ◽  
Ruoyu Chen Ruoyu Chen ◽  
Zhe Tang Zhe Tang ◽  
Hui Cang Hui Cang ◽  
Qi Xu Qi Xu
Keyword(s):  
Thermal Plasma ◽  
Active Sites ◽  
Alkali Metals ◽  
Performance Test ◽  
Catalytic Performance ◽  
Acid Sites ◽  
Efficient Catalyst ◽  
Nh3 Scr ◽  
Chemisorbed Oxygen ◽  
Non Thermal Plasma

Ce/TiO2-Palygorskite ternary composites were fabricated as an efficient catalyst for medium and low temperature NH3-SCR reaction and the optimal mass proportion (Ti:Pal=1:3) of this catalyst was confirmed by the catalytic performance test, in order to improve the surface dispersion , which needed to be further disposed by the Non-thermal plasma , after that, it was activated by thermal treatment at 400⁰C for 4 h. Based on the results obtained by XRD, FE-SEM, TEM, NH3-TPD, UV-vis (DRS), XPS, the treatment of plasma was much essential for the transformation from Ce4+ to Ce3+ on the surface of Ce/TiO2-palygorskite, to increase surface chemisorbed oxygen, and the improved dispersion, which were highly favorable for denitration. At about 350⁰C, the best NO conversion was respectively 90.59 % and 96.78 % for the untreated and treated catalysts, the latter possessed higher N2 selectivity. Besides, according to the research results on alkali metals poisoning resistance of these catalysts, it was discovered, the treated-catalyst poisoned by sodium salt had the best resistance performance, which might be related with the modification of the Non-thermal plasma, leading to more dispersed surface acid sites, to get more active sites, meanwhile, the toxicity of K was stronger than Na.

scholarly journals Mesoporous Beta Zeolite Catalysts for Benzylation of Naphthalene: Effect of Pore Structure and Acidity

Catalysts ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 504 ◽  
Author(s):  
Wenming Hao ◽  
Weimin Zhang ◽  
Zaibin Guo ◽  
Jinghong Ma ◽  
Ruifeng Li
Keyword(s):  
Catalytic Performance ◽  
Acid Sites ◽  
Zeolite Catalysts ◽  
Beta Zeolite ◽  
X Ray Diffraction ◽  
X Ray ◽  
Acid Type ◽  
Beta Zeolites ◽  
Acidic Sites ◽  
Xrd Patterns

To improve the catalytic performance of zeolite catalysts in reactions involving bulky molecules, a series of mesoporous Beta zeolite were prepared using organic functionalized fumed silica as the silicon source, which were thoroughly characterized in terms of porosity and acidity. The peaks in X-ray diffraction (XRD) patterns showed broadening, and the external surface area and mesoporosity increased progressively when the content of organic functionalization increased. An infrared (IR) spectroscopy study of adsorbed probe molecules, including pyridine (Py-IR), 2,6-ditertbutylpyridine (DTBPy-IR) and pivalonitrile (Pn-IR), showed that the improvement of mesoporosity increased the accessibility of acidic sites. In the catalytic benzylation of naphthalene with benzyl chloride (BC) over the mesoporous Beta zeolite catalysts, the conversion of BC was significantly increased when the accessibility of Brönsted acid sites improved. The increase of mesoporosity not only improved the diffusion ability of the reactants and products, but also increased the accessibility of acid sites, which greatly enhanced the activity of the mesoporous Beta zeolite catalysts. It is highlighted that the interdependence of mesoporosity, acid type, acid concentration, and strength of the mesoporous Beta zeolites on the catalytic performance in the benzylation of naphthalene with BC was comprehensively studied.

Design of composite micro/mesoporous molecular sieve catalysts

2004 ◽  
Vol 76 (9) ◽  
pp. 1647-1657 ◽  
Author(s):  
I. I. Ivanova ◽  
A. S. Kuznetsov ◽  
V. V. Yuschenko ◽  
E. E. Knyazeva
Keyword(s):  
Mesoporous Materials ◽  
Active Sites ◽  
Nitrogen Adsorption ◽  
Mesoporous Molecular Sieve ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
X Ray Diffraction ◽  
Temperature Programmed ◽  
Angle Spinning ◽  
Adsorption Desorption

Two series of composite micro/mesoporous materials with different contributions of micro- and mesoporosity were prepared by dealumination and recrystallization of mordenite zeolite. The materials were characterized by X-ray diffraction, infrared spectroscopy, 27Al magic angle spinning (MAS) NMR, nitrogen adsorption–desorption, and temperature-programmed desorption of ammonia (TPD NH3). Catalytic properties were studied in transalkylation of biphenyl with diisopropylbenzene. Both types of composite materials showed remarkably high activity, stability, and selectivity toward formation of di-isopropylbiphenyls with respect to both pure microporous and mesoporous materials. The effect is due to high zeolitic acidity combined with improved accessibility of active sites and transport of bulky molecules provided by mesopores.

The Effect of MgO Precoating on the Perfomance of Ni/MgO-Al2O3 Catalysts for Carbon Dioxide Reforming of Methane

2014 ◽  
Vol 997 ◽  
pp. 272-278 ◽  
Author(s):  
Li Qiong Huang ◽  
Zheng Hui Zhang ◽  
Zhang Long Guo
Keyword(s):  
Carbon Dioxide ◽  
Surface Area ◽  
Active Sites ◽  
Impregnation Method ◽  
X Ray Diffraction ◽  
Carbon Dioxide Reforming ◽  
Temperature Programmed ◽  
Ni Species ◽  
Adsorption Desorption ◽  
Nickel Species

Ni catalysts supported on γ?-Al2O3 supports modified by different MgO precoating weight were prepared by impregnation method. The surface area, pore diameter and Ni crystallite size were investigated by N2 adsorption/desorption (BET) and X-ray diffraction (XRD) methods. The reducing temperature and quantity information of reducible nickel species were obtained by H2-TPR experiments. The CO2 adsorption/desorption abilities of catalysts were investigated and the activity of catalysts were also measured. The coke resistance performance of catalysts for carbon dioxide reforming of methane (CDRM) was studied by CO2 temperature programmed surface reaction (CO2-TPSR). H2-TPR results revealed that there were three kinds of Ni species on the supports. Appropriate modification amount of MgO could increase the surface nickel active sites which could be easily reduced and prevented the formation of NiAl2O4 spinel species. CO2-TPD indicated that the addition of MgO increased the amount of CO2 adsorption at lower temperatures. N2 adsorption/desorption results disclosed that the excessive modification of MgO would decrease the surface area and pore size of the samples. The reforming reaction results showed that the activity was elevated from 58.62% to 65.95% over the Ni/MgO-Al2O3 when the Mg/Al ratio was 0.05 (wt.) and there was less coke evidenced by the CO2-TPSR results comparing to the Ni/γ?-Al2O3 catalyst.

Efficient Synthesis of Diethyl Carbonate by Mg, Zn Promoted Hydroxyapatite via Transesterification Reaction

2020 ◽  
Vol 18 (4) ◽  
Author(s):  
Kartikeya Shukla ◽  
Vimal Chandra Srivastava
Keyword(s):  
Thermal Analysis ◽  
Active Sites ◽  
Molar Ratio ◽  
Diethyl Carbonate ◽  
X Ray Diffraction ◽  
Reaction Conditions ◽  
X Ray ◽  
High Basicity ◽  
Temperature Programmed ◽  
Adsorption Desorption

AbstractTransesterification of propylene carbonate (PC) and ethanol is a potent non-phosgene route for the synthesis of diethyl carbonate (DEC). In the present study, hydroxyapatite was synthesized and modified using Zn and Mg (Zn/HAP and Mg/HAP). Modified hydroxyapatite was used as catalyst for the synthesis of DEC. The thermal analysis of the catalytic precursor was studied using thermogravimetric-differential thermal analysis. The structural analysis, surface morphology, and nature of active sites over the catalyst surface were studied using techniques such as Fourier transform infrared spectroscopy, X-ray diffraction, N2 adsorption-desorption, scanning electron microscopy, and CO2 temperature-programmed desorption. Effects of reaction conditions like reaction temperature, reaction time and ethanol/PC molar ratio on DEC yield were also studied. The effects of Mg and Zn on HAP were found to be promotional for the synthesis of DEC using PC and ethanol. Mg/HAP was found to be the best among the three catalysts studied owing to its high basicity. Maximum DEC yield of 52.1 % was obtained in 5 h at 433 K using Mg/HAP catalyst.

Thermally Stable Metal(Cu, Fe)-Substituted Mesoporous Aluminophosphates: Synthesis and Application as Oxidation Catalysts

2012 ◽  
Vol 550-553 ◽  
pp. 306-311 ◽  
Author(s):  
Bin Xu ◽  
Kai Feng Lin ◽  
Yan Qiu Jiang ◽  
Jian Min Sun ◽  
Xian Zhu Xu
Keyword(s):  
Thermal Stability ◽  
Active Sites ◽  
Nitrogen Adsorption ◽  
Metal Species ◽  
X Ray Diffraction ◽  
Catalytic Activities ◽  
Ft Ir ◽  
Adsorption Desorption ◽  
Ft Ir Spectroscopy ◽  
Mesoporous Aluminophosphates

Metal-substituted mesoporous aluminophosphates with high thermal stability (Fe-JLU-50 and Cu-JLU-50) has been prepared by using preformed microporous aluminophosphate precursors. The materials were characterized by X-ray diffraction, nitrogen adsorption/desorption isotherms and FT-IR spectroscopy. The characterization results showed the presence of zeolite aluminophosphate structural building units in the framework of the mesoporous aluminophosphates, which is responsible for their highly thermal stability. Also, the metal species such as Fe and Cu were successfully incorporated in the framework of the mesoporous aluminophosphates via this approach. Fe-JLU-50 and Cu-JLU-50 were evaluated in the oxidations of phenol and trimethylphenol (TMP) with aqueous H2O2, giving highly catalytic activities in both reactions. This result suggests that the materials are versatile catalysts for both small and bulky substrates, ascribed to the accessibility of the substrates to the active sites in the framework of Fe-JLU-50 and Cu-JLU-50 by the retained mesopores after calcination.

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