Chromium Oxides as Structural Modulators of Rhodium Dispersion on Ceria to Generate Active Sites for NO Reduction

ACS Catalysis ◽  
2021 ◽  
pp. 431-441
Author(s):  
Satoru Ikemoto ◽  
Satoshi Muratsugu ◽  
Takanori Koitaya ◽  
Mizuki Tada
Keyword(s):  
Active Sites ◽  
No Reduction ◽  
Chromium Oxides

Effect of Preparation Method on Cu Active Sites and the Reaction Pathway in NO Reduction by NH3 over Cu–SSZ-13

2018 ◽  
Vol 25 (4) ◽  
pp. 400-412
Author(s):  
Hao Chen ◽  
Yonghong Li ◽  
Xiaojiao Liu
Keyword(s):  
Active Sites ◽  
No Reduction ◽  
Preparation Method ◽  
Reaction Pathway

scholarly journals Kinetics of Selective Catalytic Reduction of Nitric Oxide over Pt-Cu-Zsm5 Catalyst

1970 ◽  
Vol 4 (1) ◽  
Author(s):  
Ismail Mohd Saaid ◽  
Abdul Rahman Mohamed and Subhash Bhatia
Keyword(s):  
Nitric Oxide ◽  
Selective Catalytic Reduction ◽  
Active Sites ◽  
No Reduction ◽  
Bimetallic Catalyst ◽  
Catalytic Reduction ◽  
Covalent Bond ◽  
Reaction Parameters ◽  
Heterogeneous Model ◽  
Kinetics Of

Kinetics for the selective catalytic reduction (SCR) of nitric oxide (NO) using i-C4H10 as the reducing agent over Pt-Cu-ZSM5 has been investigated in the temperature range of 200 ?C – 450 oC. Langmuir-Hinshelwood-Hougen-Watson model was proposed for kinetics of the reaction and reaction parameters were evaluated.  The heat of adsorption of NO was found to be considerably high, attributed to strong covalent bond between NO gas molecules and metal active sites.  Using reaction parameters obtained from the experiment, the heterogeneous model could form a good correlation between experimental and simulated values of NO reduction. Key Words: Reaction kinetics, Selective catalytic reduction, NO reduction, Bimetallic catalyst, H-ZSM-5 zeolite.

Active sites for NO reduction over Fe-ZSM-5 catalysts

2005 ◽  
pp. 805-807 ◽  
Author(s):  
M. Schwidder ◽  
M. Santhosh Kumar ◽  
A. Brückner ◽  
W. Grünert
Keyword(s):  
Active Sites ◽  
No Reduction

scholarly journals Identification of the Mechanism of NO Reduction with Ammonia (SCR) on Zeolite Catalysts

2020 ◽  
Author(s):  
Konstantin Khivantsev ◽  
Ja-Hun Kwak ◽  
Nicholas R. Jaegers ◽  
Miroslaw A. Derewinski ◽  
János Szanyi
Keyword(s):  
Active Sites ◽  
No Reduction ◽  
Catalytic Reduction ◽  
Molecular Nitrogen ◽  
Acid Sites ◽  
Zeolite Catalysts ◽  
Catalytic Cycle ◽  
Rate Limiting Step ◽  
Catalytically Active

<p>Cu/Zeolites catalyze selective catalytic reduction of nitric oxide with ammonia. Although the progress has been made in understanding the rate-limiting step of reaction which is reoxidation of Cu(I)(NH<sub>3</sub>)<sub>2</sub> with oxygen to restore the catalytically active Cu(II) site, the exact NO reduction chemistry remained unknown. Herein, we show that nitrosyl ions NO<sup>+</sup> in the zeolitic micropores are the true active sites for NO reduction. They react with ammonia even at below/room temperature producing molecular nitrogen through the intermediacy of N<sub>2</sub>H<sup>+</sup> cation. Isotopic experiments confirm our findings. No copper is needed for this reaction to occur. However, when NO<sup>+</sup> reacts, “freed up” Bronsted acid site gets occupied by NH<sub>3</sub> to form NH<sub>4</sub><sup>+</sup> – and so the catalytic cycle stops because NO<sup>+</sup> does not form on NH<sub>4</sub>-Zeolites due to their acid sites being already occupied. Therefore, the role of Cu(II) in Cu/Zeolite catalysts is to produce NO<sup>+</sup> by the reaction: Cu(II) + NO à Cu(I) + NO<sup>+ </sup>which we further confirm spectroscopically. The NO<sup>+</sup> then reacts with ammonia to produce nitrogen and water. Furthermore, when Cu(I) gets re-oxidized the catalytic cycle then can continue. Thus, our findings are critical for understanding complete SCR mechanism.</p>

Promotional Effect of Gadolinia on CuO Catalyst for Reduction of NO by Activated Carbon

2010 ◽  
Vol 132 ◽  
pp. 76-86
Author(s):  
Yu Ye Xue ◽  
Guan Zhong Lu ◽  
Yun Guo ◽  
Yang Long Guo ◽  
Yan Qin Wang ◽  
...  
Keyword(s):  
Activated Carbon ◽  
Active Sites ◽  
No Reduction ◽  
Catalytic Reduction ◽  
Catalytic Performance ◽  
Molar Ratio ◽  
Reduction Of No ◽  
Cooperative Effects ◽  
Promotional Effect ◽  
Catalysts For No Reduction

The Gd2O3 (gadolinia) modified CuO/AC catalysts for NO reduction by activated carbon were prepared and characterized by XRD, TPD-MS, EPR, XPS techniques. The results show that adding a small amount of Gd2O3 in the CuO catalyst can improve effectively its catalytic performance for NO reduction by activated carbon, and the appropriate molar ratio of Gd2O3/CuO is 0.03:1. The promotional effect of Gd2O3 stems from the cooperative effects between CuO and Gd2O3. The presence of Gd2O3 in the catalyst can alter the chemical state and environment of the CuO active sites and improve the catalytic activation of carbon by CuO to form more carbon reactive sites, resulting in the quicker transfer and release of oxygen decomposed from NO. The carboxylic groups on the surface of activated carbon play an important role in the catalytic reduction of NO by carbon at temperature below 300 °C.

scholarly journals Catalytic reduction of NO by CO over Pd — doped Perovskite-type catalysts

2009 ◽  
Vol 7 (4) ◽  
pp. 857-863 ◽  
Author(s):  
Mariana Khristova ◽  
Srdjan Petrović ◽  
Ana Terlecki-Baričević ◽  
Dimitar Mehandjiev
Keyword(s):  
Photoelectron Spectroscopy ◽  
Active Sites ◽  
No Reduction ◽  
Catalytic Reduction ◽  
Ethanol Solution ◽  
Direct Decomposition ◽  
X Ray ◽  
No Reduction By Co ◽  
Perovskite Type ◽  
Decomposition Of No

AbstractThe perovskite type oxides (nominal formula LaTi0.5Mg0.5O3) with addition of Pd were prepared by annealing the ethanol solution of precursors in nitrogen flow at 1200°C and characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption of NO (NO-TPD). Their activity was evaluated for NO reduction by CO under stoichiometric and oxidizing conditions and for direct decomposition of NO. Pd substituted samples exhibited high NO reduction activity and selectivity towards N2. Nearly complete elimination of NO was achieved at 200°C. Two simultaneous reactions, NO reduction by CO and direct decomposition of NO as well as two forms of NO adsorption were observed on the surface of Pd substituted perovskite samples. The distribution of Pd in different catalytically active sites or complexes on at the catalyst surface may be responsible for the proceeding of two reactions: NO reduction with CO and direct NO decomposition.

Rational design of alkali-resistant catalysts for selective NO reduction with NH3

2019 ◽  
Vol 55 (66) ◽  
pp. 9853-9856 ◽  
Author(s):  
Chao Li ◽  
Zhiwei Huang ◽  
Xiaona Liu ◽  
Junxiao Chen ◽  
Weiye Qu ◽  
...  
Keyword(s):  
Active Sites ◽  
Rational Design ◽  
No Reduction ◽  
Scr Catalysts ◽  
Trapping Sites

A rationale was proposed for designing alkali-resistant SCR catalysts, which have common characteristics of separate active sites and alkali-trapping sites.

scholarly journals Catalytic Activity of Cr2O3/sepiolite in the oxidation of benzyl alcohol

2018 ◽  
Vol 56 (3) ◽  
pp. 295
Author(s):  
Nguyen Tien Thao ◽  
Nguyen Thi Nhu ◽  
Ngo Thi Thuan
Keyword(s):  
Catalytic Activity ◽  
Reaction Time ◽  
Benzyl Alcohol ◽  
Surface Area ◽  
Active Sites ◽  
Large Surface Area ◽  
Precipitation Method ◽  
Chromium Oxides ◽  
Physical Methods ◽  
Oxidation Of Benzyl Alcohol

Cr2O3/sepiolite samples with different loadings have been prepared through the precipitation method and characterized by several physical methods such as XRD, TEM, BET, and TGA... The as-prepared materials have large surface area, high distribution of Cr2O3 nanoxides on the nanofibrous sepiolite. The catalysts have been tested in the oxidation of benzyl alcohol with t-BuOOH. Chromium oxides were found to be active sites for the oxidation of benzyl alcohol to aldehyde. The catalytic activity varied with reaction time and temperature. The appropriate temperature is about 60-70oC with conversion of 40-60% and benzaldehyde selectivity of 90%.

scholarly journals Identification of the Mechanism of NO Reduction with Ammonia (SCR) on Zeolite Catalysts

2020 ◽  
Author(s):  
Konstantin Khivantsev ◽  
Ja-Hun Kwak ◽  
Nicholas R. Jaegers ◽  
Miroslaw A. Derewinski ◽  
János Szanyi
Keyword(s):  
Active Sites ◽  
No Reduction ◽  
Catalytic Reduction ◽  
Molecular Nitrogen ◽  
Acid Sites ◽  
Zeolite Catalysts ◽  
Catalytic Cycle ◽  
Rate Limiting Step ◽  
Catalytically Active

<p>Cu/Zeolites catalyze selective catalytic reduction of nitric oxide with ammonia. Although the progress has been made in understanding the rate-limiting step of reaction which is reoxidation of Cu(I)(NH<sub>3</sub>)<sub>2</sub> with oxygen to restore the catalytically active Cu(II) site, the exact NO reduction chemistry remained unknown. Herein, we show that nitrosyl ions NO<sup>+</sup> in the zeolitic micropores are the true active sites for NO reduction. They react with ammonia even at below/room temperature producing molecular nitrogen through the intermediacy of N<sub>2</sub>H<sup>+</sup> cation. Isotopic experiments confirm our findings. No copper is needed for this reaction to occur. However, when NO<sup>+</sup> reacts, “freed up” Bronsted acid site gets occupied by NH<sub>3</sub> to form NH<sub>4</sub><sup>+</sup> – and so the catalytic cycle stops because NO<sup>+</sup> does not form on NH<sub>4</sub>-Zeolites due to their acid sites being already occupied. Therefore, the role of Cu(II) in Cu/Zeolite catalysts is to produce NO<sup>+</sup> by the reaction: Cu(II) + NO à Cu(I) + NO<sup>+ </sup>which we further confirm spectroscopically. The NO<sup>+</sup> then reacts with ammonia to produce nitrogen and water. Furthermore, when Cu(I) gets re-oxidized the catalytic cycle then can continue. Thus, our findings are critical for understanding complete SCR mechanism.</p>

scholarly journals Bimetallic AgFe Systems on Mordenite: Effect of Cation Deposition Order in the NO Reduction with C3H6/CO

Catalysts ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 58 ◽  
Author(s):  
Perla Sánchez-López ◽  
Yulia Kotolevich ◽  
Serguei Miridonov ◽  
Fernando Chávez-Rivas ◽  
Sergio Fuentes ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Inductively Coupled Plasma ◽  
Active Sites ◽  
No Reduction ◽  
Optical Emission ◽  
Reduction Reaction ◽  
Exchange Method ◽  
Inductively Coupled ◽  
Preparation Conditions ◽  
Bimetallic Systems

Mono- and bimetallic systems of Ag, Fe, and Ag–Fe exchanged in sodium mordenite zeolite were studied in the reaction of NO reduction. The transition metal cations Ag and Fe were introduced by ion exchange method both at room temperature and 60 °C; modifying the order of component deposition in bimetallic systems. These materials were characterized by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), ultraviolet-visible spectroscopy (UV-Vis), X-Ray photoelectron Spectroscopy (XPS) and High-resolution transmission electron microscopy (HR-TEM). The XPS and UV–Vis spectra of bimetallic samples revealed that under certain preparation conditions Ag+ is reduced with the participation of the Fe2+/Fe3+ ions transition and is present in the form of a Ag reduced state in different proportions of Agm clusters and Ag0 NPs, influenced by the cation deposition order. The catalytic results in the NO reduction reaction using C3H6/CO under an oxidizing atmosphere show also that the order of exchange of Ag and Fe cations in mordenite has a strong effect on catalytic active sites for the reduction of NO.

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