Duvvuri Subbarao

Correlation between Fischer-Tropsch catalytic activity and composition of catalysts

This paper presents the synthesis and characterization of monometallic and bimetallic cobalt and iron nanoparticles supported on alumina. The catalysts were prepared by a wet impregnation method. Samples were characterized using temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), CO-chemisorption, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM-EDX) and N2-adsorption analysis. Fischer-Tropsch synthesis (FTS) was carried out in a fixed-bed microreactor at 543 K and 1 atm, with H2/CO = 2 v/v and space velocity, SV = 12L/g.h. The physicochemical properties and the FTS activity of the bimetallic catalysts were analyzed and compared with those of monometallic cobalt and iron catalysts at similar operating conditions.H2-TPR analysis of cobalt catalyst indicated three temperature regions at 506°C (low), 650°C (medium) and 731°C (high). The incorporation of iron up to 30% into cobalt catalysts increased the reduction, CO chemisorption and number of cobalt active sites of the catalyst while an opposite trend was observed for the iron-riched bimetallic catalysts. The CO conversion was 6.3% and 4.6%, over the monometallic cobalt and iron catalysts, respectively. Bimetallic catalysts enhanced the CO conversion. Amongst the catalysts studied, bimetallic catalyst with the composition of 70Co30Fe showed the highest CO conversion (8.1%) while exhibiting the same product selectivity as that of monometallic Co catalyst. Monometallic iron catalyst showed the lowest selectivity for C5+ hydrocarbons (1.6%).

Development of niobium-promoted cobalt catalysts on carbon nanotubes for Fischer-Tropsch synthesis

Abstract Cobalt-based catalysts were prepared by a wet impregnation method on carbon nanotubes (CNTs) support and promoted with niobium. Samples were characterized by nitrogen adsorption, TEM, XRD, TPR, TPO and H2-TPD. Addition of niobium increased the dispersion of cobalt but decreased the catalysts reducibility. Fischer-Tropsch synthesis (FTS) was carried out in a fixed-bed microreactor at 543 K, 1 atm and H2/CO = 2 for 5 h. Addition of niobium enhanced the C5+ hydrocarbons selectivity by 39% and reduced methane selectivity by 59%. These effects were more pronounced for 0.04%Nb/Co/CNTs catalyst, compared with those observed for other niobium compositions.

Effect of niobium promoters on iron-based catalysts for Fischer-Tropsch reaction

Abstract Niobium-promoted Fe/CNT catalysts were prepared using the wet impregnation method. The samples were characterized by nitrogen adsorption, H 2 -TPR, TPD, XRD and TEM. The Fischer-Tropsch Synthesis (FTS) was carried out in a fixed-bed microreactor at 220°C, 1 atm and H 2 /CO=2 for 5 h. Addition of niobium into Fe/CNTs increased the dispersion, decreased the average size of the iron oxide nanoparticles and the catalyst reducibility. The niobium-promoted Fe catalyst resulted in appreciable increase in the selectivity of C 5+ hydrocarbons and suppressed methane formation. These effects were more pronounced for the 0.04%Nb/Fe/CNT catalyst, compared to those observed from other niobium compositions. The 0.04%Nb/Fe/CNT catalyst enhanced the C 5+ hydrocarbons selectivity by a factor of 67.5% and reduced the methane selectivity by a factor of 59.2%.

The role of support morphology on the performance of Cu/ZnO-catalyst for hydrogenation of CO2 to methanol

The effects of SBA-15 support morphology on the activity of Cu/ZnO catalyst in the hydrogenation of CO2 to methanol was investigated. In the hydrogenation of CO2 to methanol at 210°C, 2.25 MPa, H2/CO2 ratio of three remarkable difference was obtained using Cu/ZnO catalyst supported on SBA-15 with different morphology. The catalysts were characterized using N2-adsorption, field emission scanning microscopy (FESEM/EDX), transmission electron microscopy (HRTEM), and temperature-programmed reduction (TPR). Characterization of the catalyst showed that support morphology, surface area, metals dispersion, and reducibility influenced the catalytic performance. On the fiber-shaped SBA-15, copper dispersion was 29 % whereas on the spherical-shaped SBA-15, the dispersion was 20 %. The experimental results showed that the catalyst supported over fiber-shaped SBA-15 exhibit higher CO2 conversion (13.96 %) and methanol selectivity (91.32 %) compare to catalyst supported over spherical-shaped SBA-15.

Physicochemical investigations of carbon nanofiber supported Cu/ZrO2 catalyst

Zirconia-promoted copper/carbon nanofiber catalysts (Cu‐ZrO2/CNF) were prepared by the sequential deposition precipitation method. The Herringbone type of carbon nanofiber GNF-100 (Graphite nanofiber) was used as a catalyst support. Carbon nanofiber was oxidized to (CNF-O) with 5% and 65 % concentration of nitric acid (HNO3). The CNF activated with 5% HNO3 produced higher surface area which is 155 m2/g. The catalyst was characterized by X-ray Diffraction (XRD), Fourier Transform Infra-Red (FTIR) and N2 adsorption-desorption. The results showed that increase of HNO3 concentration reduced the surface area and porosity of the catalyst.

Homogeneous Deposition Precipitation Method for Synthesis of Carbon Nanofibre Based Cu-ZrO2 Catalyst for Hydrogenation of CO2 to Methanol

Deposition precipitation method was employed to synthesize carbon nanofiber based Cu-ZrO2 catalyst (Cu-ZrO2/CNF). Carbon nanofibre of herringbone type was used as a catalyst support. Prior deposition of catalyst particles, carbon nanofibre was oxidized to (CNF-O) with nitric acid solution. Catalyst was characterized by X-ray diffraction (XRD), Fourier Transmission Infrared (FTIR), Transmission Electron Microscopy (TEM) and Temperature-Programmed Reduction (TPR). Highly loaded, well-dispersed and thermally stable catalyst particles with average size of 4 nm were obtained by deposition precipitation method. Reaction studies confirmed the activity of the catalyst towards methanol formation.

Influence of Acid and Thermal Treatments on Properties of Carbon Nanotubes

The application of carbon nanotubes as a catalyst support has received considerable attention recently. The influence of acid and thermal treatments on the properties of multi-walled carbon nanotubes (MWCNTs) is presented in this paper. MWCNTs were treated with 65 wt% HNO3 at the 120 °C for 14 h in order to open the caps and introduce functional groups on the MWCNTs. Then thermal treatment was carried out at 600, 700, 800, 900 °C for 3 h in flowing Ar gas in a tubular furnace. The MWCNTs were characterized by N2- adsorption, FESEM and Raman spectroscopy. The thermal treatment resulted in slight morphological changes of the MWCNTs. The acid and thermal treatments also increased the BET surface areas and pore volumes of the MWCNTs.

Synthesis and Characterization of Bimetallic Fe/Co Nanocatalyst on CNTs for Fischer-Tropsch Reaction

Cobalt and iron are common catalysts used in the Fischer-Tropsch (FT) reaction. This paper presents the synthesis and characterization of monometallic and bimetallic cobalt and iron nanoparticles supported on carbon nanotubes (CNTs). The CNTs-supported nanocatalysts were synthesized by a wet impregnation method at various ratios of Fe:Co. The physicochemical properties of the samples were analyzed by H2-temperature programmed reduction (TPR), CO and H2-chemisorption analyses, transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. The effects of incorporation of Fe into Co on the physicochemical properties of Co/CNTs in terms of degree of reduction, CO and H2 chemisorptions and morphologies were investigated. TEM showed that metal nanoparticles were well dispersed on the external surface and inside the CNTs. For monometallic Co/CNTs and Fe/CNTs, the average metal particle size was 5±1 nm and 6±1 nm, respectively. For the bimetallic 70Co30Fe/CNTs nanocatalysts, the average particle size was found to be 4±1 nm. Metal particles attached to the outer walls were bigger than the ones inside the CNTs. H2-TPR analysis of Co/CNTs indicated two temperature regions at 330°C (low temperature) and 491°C (high temperature). The incorporation of iron into cobalt nanocatalysts of up to 30 % of the total metal loading enhanced the catalyst’s H2 and CO chemisorptions capacities and reducibility.

Swelling mechanism of urea cross-linked starch–lignin films in water

ABSTRACT Coating fertilizer particles with thin films is a possibility to control fertilizer release rates. It is observed that novel urea cross-linked starch–lignin composite thin films, prepared by solution casting, swell on coming into contact with water due to the increase in volume by water uptake by diffusion. The effect of lignin content, varied from 0% to 20% in steps of 5% at three different temperatures (25°C, 35°C and 45°C), on swelling of the film was investigated. By gravimetric analysis, the equilibrium water uptake and diffusion coefficient decrease with lignin content, indicating that the addition of lignin increases the hydrophobicity of the films. When temperature increases, the diffusion coefficient and the amount of water absorbed tend to increase. Assuming that swelling of the thin film is by water uptake by diffusion, the diffusion coefficient is estimated. The estimated diffusion coefficient decreases from 4.3 to 2.1 × 10−7 cm2/s at 25°C, from 5.3 to 2.9 × 10−7 cm2/s at 35°C and from 6.2 to 3.8 × 10−7 cm2/s at 45°C depending on the lignin content. Activation energy for the increase in diffusion coefficient with temperature is observed to be 16.55 kJ/mol. An empirical model of water uptake as a function of percentage of lignin and temperature was also developed based on Fick’s law.

Effect of Mn and Pb Promoters on the Performance of Cu/ZnO-Catalyst in CO2 Hydrogenation to Methanol

The influences of Mn or Pb promoters on the catalytic performance of Cu/ZnO-SBA-15 catalyst in the methanol synthesis from CO2 hydrogenation were studied. The catalytic performances of the prepared catalysts were investigated in a stirred high pressure reactor under conditions of T = 483K, P = 2.25 MPa, and H2:CO2 = 3:1 (volume ratio). The experimental results showed that the promoted catalysts exhibited higher catalytic performance. The Mn promoted catalyst resulted in 36% of CO2 conversion and 67% of methanol selectivity, whereas the unpromoted catalyst showed 26% of CO2 conversion and 58% of methanol selectivity.