catalyst activity
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Author(s):  
Qing Wang ◽  
Haoye Wang ◽  
Songya Qi ◽  
Zilong Su ◽  
Kaixuan Chen ◽  
...  

Abstract With the rare earth element La was selected as the A site and transition metal ions (Ni, Fe) as the B site of perovskite-type oxides with general formula ABO3, a series of LaNixFe1-xO3 (x=0, 0.3, 0.5, 0.7, 0.8, 1.0) perovskite catalysts were prepared by sol-gel method to investigate their catalytic performance for oxygen evolution reaction (OER). The catalyst activity was screened by linear scanning cyclic voltammetry (LSV), Tafel curves, and electrochemical impedance spectroscopy (EIS). A group of electrochemical tests for LaNixFe1-xO3 with various Ni/Fe ratios indicate that LaNi0.8Fe0.2O3 catalyst exhibits excellent electrochemical activity, with a resistance to charge-transfer reaction (Rct) of 5.942 Ω cm-2, overpotential of 391 mV, a Tafel slope of 102.8 mV dec-1, and electrochemical double-layer capacitance (Cdl) of 12.31 mF cm-1. The stability test after 15000 s proves that the optimized LaNi0.8Fe0.2O3 has better stability compared to pristine LaFeO3 and LaNiO3. In addition, LaNi0.8Fe0.2O3 also exhibits the largest electrochemical active area (ECSA=307.75 cm2) and exchange current density (jo=1.08 mA cm-2). This work provides reference for perovskite in improving oxygen evolution performance.


2022 ◽  
pp. 134432
Author(s):  
Nemanja Vucetic ◽  
Pasi Virtanen ◽  
Andrey Shchukarev ◽  
Tapio Salmi ◽  
Jyri-Pekka Mikkola

2022 ◽  
Vol 964 (1) ◽  
pp. 012026
Author(s):  
Nguyen Tan Luon ◽  
Le Nguyen Quang Tu ◽  
Nguyen Quang Long

Abstract Silver nanoparticles (AgNPs) are increasingly drawing a great deal of attention because of their exclusive properties and a huge variety of applications. In recent years, using AgNPs supported on various carriers as heterogeneous catalysts has become promising for treating some toxic gases in the environment, such as HCHO. This study has successfully synthesized AgNPs onto ZSM-5 microporous zeolite and ZSM-5 mesopore-modified zeolite (Meso-ZSM-5) by ion-exchange method using sodium borohydride as a reducing agent. The resulting catalysts were then characterized by N2 adsorption-desorption method. In order to evaluate HCHO adsorption, desorption, and the surface reaction of these catalysts, temperature-programmed desorption (TPD) and temperature-programmed surface reaction (TPSR) were employed. The TPD and TPSR experiments were conducted with different relative humidity. The results showed that Ag/Meso-ZSM-5 exhibited higher catalyst activity in HCHO complete oxidation than Ag/ZSM-5 at high temperatures because of a new larger pore system within the zeolite. Furthermore, TPD and TPSR experiments provided an explanation for the poor performance of the catalysts at low temperatures, which was associated with the high adsorption capacity of the zeolite.


2021 ◽  
Vol 15 (2) ◽  
pp. 141
Author(s):  
Muhammad Safaat ◽  
Indri Badria Adilina ◽  
Silvester Tursiloadi

Catalytic hydroisomerization of n-paraffin aims to produce branched paraffin isomers and suppress cracking reactions in the production of the low cloud point of biodiesel. The development of the type of metal and catalyst support, amount of metal loading, and reaction conditions are important to increase the catalyst activity. A high performace catalyst for hydroisomerization bears bifunctional characteristics with a high level of hydrogenation active sites and low acidity, maximizing the progress of hydroisomerization compared to the competitive cracking reaction. In addition, a catalyst support with smaller pore size can hinder large molecular structure isoparaffins to react on the acid site in the pore thus providing good selectivity for converting n-paraffin. Catalysts loaded with noble metals (Pt or Pd) showed significantly higher selectivity for hydroisomerization than non-noble transition metals such as Ni, Co, Mo and W. The reaction temperature and contact time are also important parameters in hydroisomerization of long chain paraffin, because long contact times and high temperatures tend to produce undesired byproducts of cracking. This review reports several examples of supported metal catalyst used in the hydroisomerization of long chain hydrocarbon n-paraffins under optimized reaction conditions, providing the best isomerization selectivity results with the lowest amount of byproducts. The role of various metals and their supports will be explained mainly for bifunctional catalysts.


Processes ◽  
2021 ◽  
Vol 10 (1) ◽  
pp. 19
Author(s):  
Alexandra Lytkina-Payen ◽  
Natalya Tabachkova ◽  
Andrey Yaroslavtsev

Methanol steam reforming (MSR) is considered an effective method for hydrogen storage and to generate high-quality hydrogen for fuel cells. In this work, a comprehensive investigation of the methanol steam reforming process using a bimetallic Pt–Rh and Cu–Ni based on different oxide supports is presented. Highly dispersed titania and zirconia doped with indium and niobium ions were synthesized by sol–gel method. The effect of the nature and quantity of the dopant cation (In, Nb) on the catalytic performance of titania supported metal catalysts was investigated. The conclusions obtained show a significant effect of both the metal alloy and the oxide support nature on the activity and selectivity of the methanol steam reforming process. Pt–Rh alloy catalyst shows higher hydrogen yield, but its selectivity in the MSR process is lower than for the catalysts containing the Cu0.8-Ni0.2 alloy. Heterovalent indium doping of titania leads to the catalytic activity increase. It was suggested that this is due to the defects formation in the oxygen TiO2 sublattice. On the contrary, the use of niobium oxide as a dopant decreases the catalyst activity in the methanol steam reforming process but leads to the selectivity increase in the studied process.


2021 ◽  
Vol 2021 ◽  
pp. 1-7
Author(s):  
Jamal Houssaini ◽  
Mohammed Naciri Bennani ◽  
Hamid Ziyat ◽  
Said Arhzaf ◽  
O. Qabaqous ◽  
...  

The self-condensation reaction of acetone, producing diacetone alcohol (DAA), is of great industrial importance. It was used to study the catalytic activity of Mg-Al catalysts synthesized by the coprecipitation method. For this purpose, we synthesized Mg-Al based hydrotalcite with a molar ratio of 3, obtained either after conventional heating or after microwave irradiation with of 100 W for three minutes. Structural and chemical properties of the obtained catalysts were characterized, using different techniques: X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), scanning electron microscope (SEM), equipped with energy dispersive X-ray (EDX), and specific surface area of the catalysts were determined by the methylene blue (MB) adsorption method. Also, these catalysts were tested in the self-condensation reaction of acetone at 273 K in the liquid phase without solvent, a reaction which requires very high catalytic activity. The microwave treatment improves the catalyst activity, and the conversion of acetone to diacetone alcohol increases from 13.2 to 18.3% after 8 h of reaction. Moreover, the microwave-treated hydrotalcite catalyst, calcined at 723 K and rehydrated under a flow of N2, is the most active and gives conversion of acetone of 52% under the same reaction conditions.


Author(s):  
Sadra Souzanchi ◽  
Laleh Nazari ◽  
Venkat Kasanneni ◽  
Zhongchao Tan ◽  
Charles Xu

Isomerization of glucose to fructose was studied over activated hydrotalcite as a catalyst in a continuous-flow tubular reactor. The synthetic hydrotalcite (HT), calcined hydrotalcite (HT-C) and activated hydrotalcite (calcined-rehydrated hydrotalcite (HT-C-R)) were characterized by TGA, XRD, BET surface area, and FT-IR analyses. The effects of operating conditions, including reaction temperature and retention time (in terms of both catalyst loading and feeding flow rate) on the isomerization reaction, were investigated. Glucose conversion and fructose selectivity were found to be more strongly dependent on retention time than reaction temperature. The fructose yield was mostly dependent on the feeding flow rate, and its maximum value of 18% corresponded to the lowest flow rate of 0.5 ml/min. The regenerated hydrotalcite catalyst showed that the catalyst activity could be restored through the calcination-rehydration process, and it showed good potential for recycling and reusability.


Energies ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 53
Author(s):  
Kai Miao ◽  
Tan Li ◽  
Jing Su ◽  
Cong Wang ◽  
Kaige Wang

Catalytic hydropyrolysis via the introduction of external hydrogen into catalytic pyrolysis process using hydrodeoxygenation catalysts is one of the major approaches of bio-oil upgrading. In this study, hydrodeoxygenation of acetone over Mo/HZSM-5 and HZSM-5 were investigated with focus on the influence of hydrogen pressure and catalyst deactivation. It is found that doped MoO3 could prolong the catalyst activity due to the suppression of coke formation. The influence of hydrogen pressure on catalytic HDO of acetone was further studied. Hydrogen pressure of 30 bar effectively prolonged catalyst activity while decreased the coke deposition over catalyst. The coke formation over the HZSM-5 and Mo/HZSM-5 under 30 bar hydrogen pressure decreased 66% and 83%, respectively, compared to that under atmospheric hydrogen pressure. Compared to the test with the HZSM-5, 35% higher yield of aliphatics and 60% lower coke were obtained from the Mo/HZSM-5 under 30 bar hydrogen pressure. Characterization of the spent Mo/HZSM-5 catalyst revealed the deactivation was mainly due to the carbon deposition blocking the micropores and Bronsted acid sites. Mo/HZSM-5 was proved to be potentially enhanced production of hydrocarbons.


2021 ◽  
Author(s):  
Toyin Omojola

Modern operando spectroscopy and microscopy, and kinetic investigations have provided qualitative evidence for active site dynamics, catalyst surface dynamics, and charge transport. On the macroscale, intraparticle and interparticle mass and heat transfer can be tuned to optimise selectivity over heterogeneous catalysts. On the microscale, adsorbate-induced restructuring, adsorbate mobility, surface composition, oxidation states, charge transport, bandgap, and the degree of coordination of the active site have been identified for controlling product selectivity. There exist, however, limited physics-based and data-driven multiscale models that can assimilate these qualitative descriptors in an integrated manner to extract quantitative catalyst activity, stability, and product selectivity descriptors. A multiscale model, which describes the evolution of gas species, adspecie accumulation due to reactivity, stability, lifetime, and mobility, charge transport involving electrons and holes, heat transfer for non-isothermal conditions due to reaction exothermicity, and the changing catalyst states is provided. Dynamical effects are included in these models to bridge the gap between laboratory-scale studies and industrial technical reactors.


Author(s):  
И.А. Щурова ◽  
Н.А. Алексеева ◽  
С.В. Сысолятин ◽  
В.В. Малыхин

Статья посвящена усовершенствованию способа получения 2,4,6-тригидрокситолуола, востребованного химического реагента в синтезе азокрасителей и пигментов, а также химико-фармацевтических препаратов и различных полимеров. Основным сырьем для его получения является 2,4,6-тринитротолуол, который подвергают каталитическому гидрированию с последующим гидролизом образовавшегося 2,4,6-триаминотолуола. В данной работе предложены условия многоциклового использования палладиевого катализатора гидрирования 2,4,6-тринитротолуола, позволяющие сохранять активность катализатора и повысить выход 2,4,6-триаминотолуола выше 98 %. Аминопроизводное выделяется в виде дисульфата действием концентрированной серной кислоты. Кроме того, изучено влияние соотношения вода/дисульфат 2,4,6-триаминотолуола на выход 2,4,6-тригидрокситолуола; найдены условия, в которых выход на стадии гидролиза увеличен до 83-84 %. Проведен сравнительный анализ различных способов выделения 2,4,6-тригидрокситолуола из реакционной массы. The paper is concerned with upgrading the synthetic method for 2,4,6-trihydroxytoluene, an in-demand chemical reactant in the synthesis of azo-dyes and pigments, as well as chemical pharmaceuticals and various polymers. The basic feedstock for the synthesis thereof is 2,4,6-trinitrotoluene, which is subjected to catalytic hydrogenation followed by hydrolysis of the resulting 2,4,6-triaminotoluene. Here we suggest conditions for the multicycle use of Pd catalyst employed for the hydrogenation of 2,4,6-trinitrotoluene, which allow the catalyst activity to be retained and the yield of 2,4,6-triaminotoluene to be enhanced above 98%. The amino derivative is liberated as the disulfate by concentrated sulfuric acid. Moreover, we examined how the ratio of water / 2,4,6-triaminotoluene disulfate influences the yield of 2,4,6-trihydroxytoluene. Conditions were found in which the yield from hydrolysis is 83-84 %. Different methods for the isolation of 2,4,6-trihydroxytoluene from the reaction mixture were comparatively analyzed.


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