Catalyst Crystallite Size Research Articles

Dependence of wustite-based iron catalyst crystallite size on ammonia synthesis reaction analysed by in situ XRPD

Dependence of wustite-based iron catalyst crystallite size on ammonia synthesis reaction analysed by <i>in situ</i> XRPD

Preparation and Characterization of Mixed-Oxide Catalyst

Solid heterogeneous CuO-MoO3/ZrO2 catalyst was prepared by impregnation using suitable precursor materials supported over zirconia. Upon calcination at 450°C for 2 hours, available techniques were employed for the characterization. The available oxides and minerals in the catalyst were revealed by the XRF and XRD profiles respectively. The catalyst crystallite size (131.6nm) was obtained using the Bragg’s equation from the latter. Thermal analysis showed three weight loss stages between (49.25-152.06°C), (152.06-559.47°C) and (559.47-752.0°C) while presence of sulphate and zirconia oxides was revealed by the FTIR analysis due to appearance of absorption bands around 1225-980cm-1 and 700-600 cm-1 respectively.

Mixed-Metal Oxide Catalyst for Liquid Phase Benzene Alkylation

Development of cheaper, active and more ecofriendly heterogeneous acid catalyst is a challenge mitigating the petrochemical industries. CuO-MoO3/ZrO2 solid catalyst was prepared by impregnation using suitable precursor materials supported over zirconia. Upon calcination at 450°C for 2 h and activation (by soaking in 2M H2SO4 for 30 minutes), available techniques were employed for the characterization. The available oxides and minerals in the catalyst were revealed by the XRF and XRD profiles respectively. The catalyst crystallite size (131.6nm) was obtained using the Bragg’s equation from the latter. Thermal analysis showed three weight loss stages between (49.25-152.06°C), (152.06-559.47°C) and (559.47-752.0°C ) while presence of sulphate and zirconia oxides was revealed by the FTIR analysis due to appearance of absorption bands around 1225-980cm-1 and 700-600cm-1 respectively. The catalyst (1wt%) was tested for alkylation in a continuous stirred reactor at 80°C using variable (2:1, 4:1 and 10:1) benzene to 1-decene molar ratios. The effects of reaction time and molar ratios on the selectivity, conversion and yield were determined. The alkylation results showed that the catalyst is highly selective to 1-decylbenzene as low amount of side products was obtained. The product yield and conversion increased with reaction time and benzene /1-decene molar ratio while selectivity decreased with increase in benzene /1-decene molar ratio with time.

Highly efficient COx-free hydrogen evolution activity on rod Fe2N catalysts for ammonia decomposition

The morphology of Fe2O3 precursors had a significant effect on the Fe2N catalyst crystallite size, components and activity.

Selective hydrodealkylation of C9+ aromatics to benzene, toluene, and xylenes (BTX) over a Pt/H-ZSM-5 catalyst

Pt/H-ZSM-5 zeolites (Si/Al ratio of 50) with a Pt loading of 0.28wt.% were successfully synthesized and employed as catalysts for the selective hydrodealkylation of C9+ aromatics to benzene, toluene, and xylenes (BTX). Five different crystallite sizes (40, 20, 10, 5, 2μm) were prepared using different aging times before crystallization. The influence of crystallite size on catalytic activity was investigated, and the catalysts synthesized were physicochemically characterized by XRD, BET, SEM, and ICP-OES. Hydrodealkylation was performed in a conventional fixed bed reactor, and the influences of crystallite size on ethyltoluene (ET) isomer conversion and on the recovery yields of trimethylbenzene (TMB) isomers were examined. Conversion of ET isomers was always higher than that of TMB isomers. The distribution of products obtained was strongly influenced by Pt/H-ZSM-5 crystallite size, that is, ET isomer conversion decreased and TMB isomer recovery yield increased with crystallite size. Catalyst crystallite size was found to dictate catalytic activity with respect to selective hydrodealkylation. Pt/H-ZSM-5 with a crystallite size of 5μm exhibited the best catalytic performance for the selective hydrodealkylation of C9+ aromatics to BTX.

Pt electrodeposited over carbon nano-networks grown on carbon paper as durable catalyst for PEM fuel cells

We propose an innovative 3-step manufacturing technique for the synthesis of the catalyst layer of proton exchange membrane electrodes directly over a gas diffusion layer consisting of carbon paper (CP). In the first step, a carbon synthesis catalyst was formed in a bicontinuous microemulsion. In the second step, carbon nano-networks (CNNs) were directly grown over CP by thermal chemical vapor deposition of ethene over the metal catalyst embedded in the simultaneously carbonized microemulsion matrix. In the third step, the electrocatalyst, here Pt, was deposited on the CNNs. The influence of surfactant type, Na-AOT or Triton X-100, carbon synthesis catalyst type, Fe, Co or Pt, and loading on the electrolyte accessible surface area (ESA) and carbon corrosion resistance was evaluated in a three-electrode half-cell. CNNs grown from Fe and synthetized in Na-AOT microemulsions resulted as the best combination in terms of ESA and carbon corrosion resistance and were used for subsequent investigations. The CNNs grown on CP (CNNs/CP) were electrochemically oxidized prior to Pt electro-deposition by means of potential cycling. The effect of oxidation of the CNNs on the size and spatial distribution of the electrodeposited Pt catalyst was evaluated. Increasing the number of functionalizing oxidation cycles from 0 to 100 decreased the average catalyst crystallite size from 19 to 9nm. The CNNs/CP samples showing the highest electrochemically active surface area (ECSA) were compared to a commercial catalyst with respect to ECSA, catalyst utilization, and durability to potential cycling. The ECSA for the CNNs/CP samples turned out to be lower than that of the commercial catalyst due to the larger catalyst size. On the other hand, the CNN/CP samples proved to be more durable and higher Pt utilization was achieved.

Synthesis, characterization and electrochemical studies of Pt-W/C catalyst for polymer electrolyte membrane fuel cells

Pt-W/C catalyst was synthesized by slow reduction of platinum and tungsten solutions in the desired ratio with subsequent deposition on the Vulcan carbon already added to the solution. Crystallite size of catalyst was about 9 nm and its density, cell volume, d-spacing and lattice parameter were also calculated. EDX analysis of the catalyst was also done. Electrochemical surface area of the catalyst was determined by cyclic voltammetry (CV). CV of the catalyst was done both in acidic and basic media to find out the peak potential, peak current, specific activity and mass activity of the catalyst. Peak potential versus scan rate plots showed that the electro oxidation of methanol is an irreversible process. Tafel equation was used to plot polarization curves to find out the exchange current density. Higher values of exchange current indicate better catalysts. Specific activities of the catalyst were determined in acidic and basic media and it was found that the specific activity in basic media increased substantially as compared to acidic media. The specific activity in acidic media was 83 mA/mg pt whereas in basic media it was 137mA/mg pt which is a substantial increase. Heterogeneous rate constant in acidic media was 6.15 x 10−6 cm/ s and in basic media it was 4.92 x 10−5 cm/s which is much higher in basic media. In this binary catalyst addition of tungsten has increased the catalytic activity but it is non-noble metal thus will decrease the cost. Stability studies of the catalyst were done upto fifty cycles both in acidic and basic media and was found quite stable in both the media.

Effect of manganese on the catalytic performance of an iron-manganese bimetallic catalyst for light olefin synthesis

A systematic study was carried out to investigate the promotion effect of manganese on the performance of a coprecipitated iron-manganese bimetallic catalyst for the light olefins synthesis from syngas. The catalyst samples were characterized by N2 physisorption, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), Mössbauer spectroscopy, H2-differential thermogravimetric analysis (H2-DTG), CO temperature-programmed reduction (CO-TPR) and CO2 temperature-programmed desorption (CO2-TPD). The Fischer-Tropsch synthesis (FTS) performance of the catalyst was measured at 1.5 MPa, 250 °C and syngas with H2/CO ratio of 2.0. The characterization results indicated that the addition of manganese decreases the catalyst crystallite size, and improves the catalyst BET surface area and pore volume. The presence of manganese suppresses the catalyst reduction and carburization in H2, CO and syngas, respectively. The addition of manganese improves the catalytic activity of water-gas shift reaction and suppresses the oxidation of iron carbides in the FTS reaction. The incorporation of manganese improves the catalyst surface basicity and results in a significant improvement in the selectivities to light olefins and heavy hydrocarbons (C5+), and furthermore an inhibition of methane formation in FTS. The pure iron catalyst (Mn-00) has the highest initial FTS catalytic activity (65%) and the lowest selectivity (17.35 wt%) to light olefins (C=2−C=4). The addition of an appropriate amount of manganese can improve the catalyst FTS activity.

D-57 Alumina-Supported Palladium Catalyst Crystallite Size Determination by EXAFS, XRD, and TEM

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99/03625 Three-phase flow characteristics in a direct coal liquefaction reactor: Idogawa, K. Hokkaido Kogyo Gijutsu Kenkyusho Hokoku, 1999, 72, 1–12. (In Japanese)

A systematic study was carried out to investigate the promotion effect of manganese on the performance of a coprecipitated iron-manganese bimetallic catalyst for the light olefins synthesis from syngas. The catalyst samples were characterized by N2 physisorption, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), Mössbauer spectroscopy, H2-differential thermogravimetric analysis (H2-DTG), CO temperature-programmed reduction (CO-TPR) and CO2 temperature-programmed desorption (CO2-TPD). The Fischer-Tropsch synthesis (FTS) performance of the catalyst was measured at 1.5 MPa, 250 °C and syngas with H2/CO ratio of 2.0. The characterization results indicated that the addition of manganese decreases the catalyst crystallite size, and improves the catalyst BET surface area and pore volume. The presence of manganese suppresses the catalyst reduction and carburization in H2, CO and syngas, respectively. The addition of manganese improves the catalytic activity of water-gas shift reaction and suppresses the oxidation of iron carbides in the FTS reaction. The incorporation of manganese improves the catalyst surface basicity and results in a significant improvement in the selectivities to light olefins and heavy hydrocarbons (C5+), and furthermore an inhibition of methane formation in FTS. The pure iron catalyst (Mn-00) has the highest initial FTS catalytic activity (65%) and the lowest selectivity (17.35 wt%) to light olefins (C=2−C=4). The addition of an appropriate amount of manganese can improve the catalyst FTS activity.

Preparation, characterisation and catalytic behaviour of cobalt–niobia catalysts

Cobalt–niobia catalysts were prepared using the colloidal sol–gel technique. Niobium chloride or niobia oxide were used as precursor. The differences between the procedures used are due to the methods of preparation of the colloidal suspensions and gelification. The catalysts were characterised using adsorption and desorption curves of Kr and N 2 at 77 K, H 2-Chemisorption, XRD, FT-IR, XPS and electron microscopy investigations. Preparation of these catalysts without experimental precautions led to a very inhomogeneous structural and textural material. In contrast, the colloidal sol–gel technique controls both the structure of the niobia oxide and the tailoring of cobalt. A strong metal support interaction effect (SMSI) was present irrespective of the sample preparation variant. Although the rate of butane hydrogenolysis was low for all catalysts, a correlation between TOF and the catalyst crystallite size was found. Selectivity to methane, ethane, propane or to isomerization also depends on the catalyst crystallite size.

ROLE OF IN-SITU PRODUCED METHANOL ON THE CATALYST DEACTIVATION IN THE LIQUID PHASE METHANOL SYNTHESIS PROCESS

ABSTRACT The role of methanol produced in-situ in the liquid phase methanol synthesis process has been experimentally examined. The catalyst crystallite size is found to be more stable when the produced water and methanol are consistently removed from the catalyst active sites. The experimental evidence shows that in-situ produced water is not the only culprit for the catalyst crystallite size growth, rather, methanol is also responsible for contributing to crystallite growth and therefore catalyst deactivation Hydrothermal leaching of the catalyst was also determined to be an active participant in catalyst deactivation. Two experimental designs were run to assess the influence of temperature, leaching solution concentration and pretreatment conditions on the extent of leaching of the methanol synthesis catalyst. Water and methanol were found to be active participants in the reduction of catalyst activity. Hence, the methanol/water solutions serve as potentially harmful agents in the leaching of aluminum ...

Effect of catalyst dispersion on coal liquefaction with iron catalysts

The effectiveness of fine particle iron catalysts for first-stage coal liquefaction is influenced by the dispersion of the catalyst. Dispersion can be characterized by catalyst surface area, particle size, and crystallite size. Increasing catalyst dispersion by increasing catalyst surface area, and decreasing catalyst particle size and/or decreasing catalyst crystallite size, results in higher levels of coal conversion to soluble products. For iron systems, a distinction must be made between the catalyst precursor and the active catalyst. Coal impregnation with iron catalyst precursors results in higher coal conversion than simple mixing of powdered catalyst precursors with coal. Impregnation of iron precursors onto coal affects catalyst dispersion by maintaining the fine particle size of the precursor during the transformation to the active catalyst phase