Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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A series of Au/TiO2 catalysts were prepared by either photodeposition or deposition-precipitation methods. The catalysts were characterized by inductively coupled plasma-mass spectrometry (ICP-MS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The catalytic performance of these catalysts was investigated by preferential oxidation of carbon monoxide in a hydrogen stream. A high gold dispersion and narrow size distribution was obtained for Au/TiO2 catalysts prepared by both photodeposition or deposition-precipitation methods. The photodeposition method facilitates the preparation of gold particles as small as 1.5 nm on the support, whereas in the deposition-precipitation method, the gold particles were found to be around 2-3 nm. The catalyst prepared by the photodeposition method showed higher CO conversion and CO selectivity than those prepared by the deposition- precipitation method. The selectivity of CO reacting with O2 decreased with increasing reaction temperature due to H2 competing with CO at high temperatures. Au/TiO2 catalysts prepared by the photodeposition method showed relatively higher CO selectivity below 65 °C when compared with the deposition-precipitation method. The differences in activity could be attributed to the difference in chemical state of gold particles and the particle size of gold. The catalyst prepared by photodeposition had a smaller particle size (1.5 nm). It had higher CO conversion at low temperature (&lt;50 °C). However, the CO conversion and CO selectivity is low between 50 and 100 °C. ©2009 American Chemical Society.

Chemistry

School of Advanced Sciences

Chennai Campus

World University root node

Industrial and Engineering Chemistry Research

Preferential oxidation of CO in H2 stream on Au/TiO2 Catalysts: Effect of preparation method

A series of gold catalysts supported on Fe2O3- TiO2 with various iron contents were prepared. A FeOx-TiO2 support was prepared via incipient-wetness impregnation with aqueous solution of Fe(NO3)3 on TiO2. A gold catalyst with a nominal loading of 1 wt % was prepared by deposition-precipitation at pH 7 and 65 °C. The catalysts were characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The catalytic performance of these catalysts were investigated by preferential oxidation of carbon monoxide in hydrogen stream (PROX). The reaction was conducted in a fixed-bed microreactor with a feed of CO:O2:H2:He ) 1:1:49:49 (volume ratios). A limited amount of oxygen was used. Gold catalysts have been reported to be efficient catalysts for the PROX reaction to reduce CO concentration to &gt;50 ppm. The Au/TiO2 catalyst had high CO and H2 oxidation activity. However, CO conversion decreases obviously when the temperature reaches above 80 °C, because of the competition of hydrogen oxidation on the catalysts. In this study, FeOx was added to Au/TiO2 to suppress H2oxidation without sacrificing the activity for CO oxidation. Adding a suitable amount of Fe2O3 on Au/TiO2 could enhance CO conversion to a higher extent and suppress H2 oxidation. In the highly active gold-supported catalysts, the amorphous nature of Fe2O3, along with TiO2, not only enhanced electronic interaction but also stabilized the nanosized gold particles, thereby enhancing the catalytic activity of CO oxidation toward a higher extent. © 2009 American Chemical Society.

Au/FeOx-TiO2 catalysts for the preferential oxidation of CO in a H2 stream

A series of Au/TiO2 catalysts were prepared by photo-deposition (PD) method. Various preparation parameters, such as pH value, power of UV light and irradiation time on the characteristics of the catalysts were investigated. The catalysts were characterized by inductively-coupled plasma-mass spectrometry, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and high-resolution transmission electron microscopy. The preferential oxidation of CO in H2 stream (PROX) on these catalysts was carried out in a fixed-bed micro reactor with a feed of CO: O2: H2: He = 1: 1: 49: 49 (volume ratios) and a space velocity of 30,000 ml/g h. Limited amount of O2 was used to investigate the selectivity of O2 reacting with CO or H2. Au/TiO2 catalysts prepared by PD method showed narrow particle size distribution of gold particles within few nanometers and were found to be ∼1.5 nm. The particle size of gold nanoparticles deposited on the support depends on irradiation time, UV light source and pH value of preparation. The electronic structure of Au was a function of particle size. The smaller the Au particle size was, the higher the concentration of Au cation was. Using weak power of UV light, appropriate irradiation time and suitable pH value, very fine gold particles on the support could be obtained even in the powder form. The samples prepared with PD method did not need heat treatment to reduce Au cation, UV irradiation could reduce it. Therefore it is easier to have smaller particle size. Au/TiO2 catalysts prepared by PD method were very active and selective in PROX reaction. In long time test, the catalysts were stable at 80 °C for more than 60 h. © 2009 Professor T. Nejat Veziroglu.

International Journal of Hydrogen Energy

Au/TiO2 catalysts prepared by photo-deposition method for selective CO oxidation in H2 stream

Vapor phase hydrogenation of nitrobenzene is reported on 1 wt.% Pd supported on hydrotalcite, MgO and γ-Al2O3 catalysts. The catalysts were prepared in the laboratory using a wet impregnation method and were characterized by XRD, BET surface area, TPR, TEM, XPS and CO chemisorption studies. The conversion of nitrobenzene was studied in the temperature region of 498-573 K and compared on all the catalysts. An impressive catalytic performance of nitrobenzene conversion was observed on hydrotalcite supported Pd catalyst. CO chemisorption and TEM results prove that palladium disperses better on hydrotalcite supports when compared with other conventional supports such as MgO and γ-Al2O3, which is responsible for the high conversion of nitrobenzene. © 2008 Elsevier B.V. All rights reserved.

Applied Catalysis A: General

Hydrogenation of nitrobenzene over palladium-supported catalysts-Effect of support

Vapour phase oxidation of tetralin to 1-tetralone using molecular oxygen is reported for the first time on Cr and Fe substituted MCM-41 molecular sieves. Mesoporous monometallic Cr-MCM-41(Si/Cr 25, 50, 75 and 100), Fe-MCM-41(Si/Fe = 25) and bimetallic Cr-Fe-MCM-41(Si/(Cr + Fe) = 100) molecular sieves were synthesized by direct hydrothermal (DHT) process and characterized by XRD, ICP-AES, DR-UV-vis spectroscopy, EPR spectroscopy and SEM techniques. The conversion of tetralin and the selectivity for 1-tetralone were studied in the temperature range of 473-623 K. The efficiency of all the catalysts was evaluated and compared for the oxidation reaction under atmospheric pressure. Among various catalysts under study, Cr-MCM-41catalyst with Si/Cr = 25 exhibited maximum efficiency. The correlation between 1-tetralone selectivity and the catalysts physico-chemical characteristics is made. A reaction scheme is proposed for the oxidation of tetralin to 1-tetralone. The reaction is considered to occur in two steps: oxidation of tetralin to tetralol and oxidation of the latter to 1-tetralone, with the former process occurring over Cr3+ and the latter over Cr6+. © 2007 Elsevier B.V. All rights reserved.

Journal of Molecular Catalysis A: Chemical

Vapour phase oxidation of tetralin over Cr and Fe substituted MCM-41 molecular sieves

Pd supported on Mg-Al hydrotalcite with different Pd loadings (0.5, 1, 2 and 5 wt.% of Pd) prepared by impregnation method were characterized by XRD, BET Surface area, CO chemisorption and TPR. The catalyst activity was studied for vapor phase hydrogenation of nitrobenzene at atmospheric pressure in the temperature range of 498-598 K. The metallic dispersion, was obtained by CO chemisorption studies. Pd particle size before and after the reaction was calculated from XRD data. From the TPR studies, it was observed that the negative signal due to the decomposition of PdHx in the low temperature region was absent due to the smaller particle size of the Pd. XRD result also indicate the presence of smaller Pd particle size in low Pd loadings which increases with Pd loading. It was observed that very low concentration of Pd supported on hydrotalcite (0.5 wt.% Pd/HT) is sufficient to get high activity towards the hydrogenation of nitrobenzene to aniline (conversion = 97% and selectivity = 98%) at 498 K. The higher activity of this catalyst was attributed to higher dispersion and lower particle size of Pd as observed from CO chemisorption and XRD results. The particle size of Pd before and after reaction is more or less same indicating that the deactivation is not due to Pd agglomeration but due to the poisoning effect of water generated during the course of the reaction. The reconstruction of hydrotalcite structure in the spent catalysts as evidenced by XRD is indication that water is formed during the reaction. © 2007 Elsevier B.V. All rights reserved.