On the Nature of the Lewis Acidic Sites in “TMA-Free” Phenol-Modified Methylaluminoxane

2019 ◽  
Vol 2020 (11-12) ◽  
pp. 1088-1095 ◽  
Author(s):  
Francesco Zaccaria ◽  
Cristiano Zuccaccia ◽  
Roberta Cipullo ◽  
Peter H. M. Budzelaar ◽  
Alceo Macchioni ◽  
...  
Keyword(s):  
Free Phenol ◽  
Lewis Acidic Sites ◽  
Acidic Sites

scholarly journals Effect of Fe Additives on the Catalytic Performance of Ion-Exchanged CsX Zeolites for Side-Chain Alkylation of Toluene with Methanol

Catalysts ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 829 ◽  
Author(s):  
Zhang ◽  
Yuan ◽  
Miao ◽  
Li ◽  
Shan ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Catalytic Performance ◽  
High Yield ◽  
Side Chain ◽  
Impregnation Method ◽  
Basic Sites ◽  
Lewis Acidic Sites ◽  
X Zeolite ◽  
Acidic Sites ◽  
Negative Effect

The side-chain alkylation of toluene with methanol was investigated over some Fe-modified Cs ion-exchanged X zeolite (CsX) catalysts prepared via the impregnation method using different iron sources. The absorption/activation behaviors of the reactants on the surface of the catalysts were studied by in situ Fourier-transform infrared (FT-IR) spectroscopy and temperature programmed desorption (TPD) mass measurements. Modification of CsX with a small amount of FeCl3 could result in a considerable decrease in catalytic activity, due mainly to the remarkable decrease in the density of acidic and basic sites of the catalysts. Interestingly, the Fe(NO3)3-modified CsX with an optimum Fe loading of 0.15 wt.% shows improved catalytic activity and high yield compared to the side-chain alkylation products. Modification of CsX with Fe(NO3)3 could also result in a decrease in basic sites of the catalyst. However, such a change does not bring an obvious negative effect on the adsorption/activation of toluene, while it could effectively inhibit the generation of the undesired bidentate formate. Furthermore, the introduced FeOx species (derived from the decomposition of Fe(NO3)3) may also act as new Lewis acidic sites to participate in the activation of methanol and to stabilize the formed active intermediates (i.e., unidentate formate). Therefore, modification of CsX with a suitable amount of Fe(NO3)3 may adjust its adsorption/activation ability for reagents by changing the acid–base properties of the catalyst, which can finally enhance the catalytic performance for the side-chain alkylation of toluene with methanol.

scholarly journals Low Temperature NH3-SCR over Mn-Ce Oxides Supported on MCM-41 from Diatomite

Materials ◽  
2019 ◽  
Vol 12 (22) ◽  
pp. 3654 ◽  
Author(s):  
Mingxuan Ma ◽  
Xiaoyu Ma ◽  
Suping Cui ◽  
Tingting Liu ◽  
Yingliang Tian ◽  
...  
Keyword(s):  
Molecular Sieves ◽  
Synthesis Method ◽  
Molar Ratio ◽  
Impregnation Method ◽  
Catalyst Carrier ◽  
Nh3 Scr ◽  
Catalytic Material ◽  
Lewis Acidic Sites ◽  
Acidic Sites ◽  
Mcm 41

A series of MCM-41 molecular sieves with different molar ratio of template to silicon were synthesized through hydrothermal synthesis method by using cetyltrimethylammonium bromide (CTAB) as the template, diatomite as the silicon source. By using impregnation method, the Mn-Ce/MCM-41 SCR molecular sieve-based catalysts were prepared. The results observed that when the molar ratio of template to silicon was 0.2:1, the MCM-41 as catalyst carrier has the highest surface area and largest pore volume, it also presented typically ordered hexagonal arrays of uniform channels. The denitration catalytic material based on this carrier has a high number of Lewis acidic sites, and the denitration efficiency can reach more than 93%.

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.

Exploring the Role of Hexanuclear Clusters as Lewis Acidic Sites in Isostructural Metal–Organic Frameworks

2019 ◽  
Vol 31 (11) ◽  
pp. 4166-4172 ◽  
Author(s):  
Jiafei Lyu ◽  
Xuan Zhang ◽  
Peng Li ◽  
Xingjie Wang ◽  
Cassandra T. Buru ◽  
...  
Keyword(s):  
Metal Organic Frameworks ◽  
Hexanuclear Clusters ◽  
Lewis Acidic Sites ◽  
Acidic Sites ◽  
Metal Organic

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.

Mo CNDO/2 studies of NH3 adsorption on Lewis acidic sites ofγ-Al2O3 surface

1984 ◽  
Vol 24 (1-2) ◽  
pp. 25-29 ◽  
Author(s):  
M. B. Fleisher ◽  
L. O. Golender ◽  
M. V. Shimanskaya
Keyword(s):  
Nh3 Adsorption ◽  
Lewis Acidic Sites ◽  
Acidic Sites

Catalyzing Cascade Production of Methyl Levulinate from Polysaccharides Using Heteropolyacids HnPW11MO39with Brønsted/Lewis Acidic Sites

2017 ◽  
Vol 6 (1) ◽  
pp. 165-176 ◽  
Author(s):  
Xueyan Zhang ◽  
Yue Li ◽  
Lifang Xue ◽  
Shengtian Wang ◽  
Xiaohong Wang ◽  
...  
Keyword(s):  
Methyl Levulinate ◽  
Lewis Acidic Sites ◽  
Acidic Sites

scholarly journals Thermodynamically driven self-formation of Ag nanoparticles in Zn-embedded carbon nanofibers for efficient electrochemical CO2 reduction

RSC Advances ◽  
2021 ◽  
Vol 11 (40) ◽  
pp. 24702-24708
Author(s):  
Gi-Baek Lee ◽  
In-Kyoung Ahn ◽  
Won-Hyo Joo ◽  
Jae-Chan Lee ◽  
Ji-Yong Kim ◽  
...  
Keyword(s):  
Ag Nanoparticles ◽  
Carbon Nanofiber ◽  
Co2 Reduction ◽  
Reduction Reaction ◽  
One Pot ◽  
Electrochemical Co2 Reduction ◽  
Lewis Acidic Sites ◽  
Acidic Sites ◽  
Forming Strategy ◽  
Reaction Performance

Ag nanoparticles in Zn-embedded carbon nanofiber were synthesized by a simple one-pot, self-forming strategy. Charged Zn single atoms act as Lewis acidic sites and improving the CO2 reduction reaction performance of the Ag nanoparticles.

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