Catalyst Grain Size Research Articles

Simultaneous production of syngas and carbon nanotubes from CO2/CH4 mixture over high-performance NiMo/MgO catalyst

Direct conversion of biogas via the integrative process of dry reforming of methane (DRM) and catalytic methane decomposition (CDM) has received a great attention as a promising green catalytic process for simultaneous production of syngas and carbon nanotubes (CNTs). In this work, the effects of reaction temperature of 700–1100 °C and CH4/CO2 ratio of biogas were investigated over NiMo/MgO catalyst in a fixed bed reactor under industrial feed condition of pure biogas. The reaction at 700 °C showed a rapid catalyst deactivation within 3 h due to the formation of amorphous carbon on catalyst surface. At higher temperature of 800–900 °C, the catalyst can perform the excellent performance for producing syngas and carbon nanotubes. Interestingly, the smallest diameter and the highest graphitization of CNTs was obtained at high temperature of 1000 °C, while elevating temperature to 1100 °C leads to agglomeration of Ni particles, resulting in a larger size of CNTs. The reaction temperature exhibits optimum at 800 °C, providing the highest CNTs yield with high graphitization, high syngas purity up to 90.04% with H2/CO ratio of 1.1, and high biogas conversion (XCH4 = 86.44%, XCO2 = 95.62%) with stable performance over 3 h. The typical composition biogas (CH4/CO2 = 1.5) is favorable for the integration process, while the CO2 rich biogas caused a larger grain size of catalyst and a formation of molybdenum oxide nanorods (MoO3). The long-term stability of NiMo/MgO catalyst at 800 °C showed a stable trend (> 20 h). The experimental findings confirm that NiMo/MgO can perform the excellent activity and high stability at the optimum condition, allowing the process to be more promising for practical applications.

Integrating calcium-looping and reverse-water–gas-shift reaction for CO2 capture and conversion: Screening of optimum catalyst

Integrating calcium-looping cycle (CaL) with reverse-water–gas-shift (RWGS) reaction represents an effective path to realizing integrated CO2 capture and utilization (ICCU). Screening a suitable catalyst to construct highly efficient CaO-based dual function materials (DFMs) is essential for CaL-RWGS. In the current work, M@CaO (M = Ni, Co, Mn, and Fe) DFMs are prepared for CaL-RWGS, and the influence of catalyst component on the structure, CO2 capture and RWGS performance, and kinetic behaviors of the CaO-based DFMs is investigated. Results show that the interaction between CaO and catalyst affects the average grain size and dispersion of metallic catalyst, oxygen vacancy concentration, surface basicity, and reducibility of CaO-based DFMs. The desired Mn@CaO DFMs exhibit outstanding CaL-RWGS performance at 650 °C, 15%CO2 and 50%H2, with a great CO2 uptake (12.30 mmol CO2/g), a favorable CO yield (5.92 mmol CO/g), and an impressive CO2 conversion (53.53%), as well as a high CO selectivity (89.98%). Furthermore, Mn@CaO exhibits excellent carbonation and regeneration kinetics but inferior working stability for CO2 capture and CO production in multiple CaL-RWGS cycles. Overall, Mn could be a competitive and cost-effective catalyst candidate for high-performance CaO-based DFMs for CaL-RWGS applications, while further work is needed to improve cyclic stability.

Improvement of Cu-SAPO-34 hydrothermal stability by tuning P/Al ratio for selective catalytic reduction of NO by NH3

Cu-SAPO-34 is a promising catalyst for abatement of NO via selective catalytic reduction with NH3 (NH3-SCR), but its hydrothermal stability needs to be enhanced. In this work, the Cu-SAPO-34 catalysts with different P/Al ratios of 0.8, 1.0 and 1.2 were prepared, and the temperature window with NO conversion >90% (T90) for all catalysts were similar (160–570 °C). The T90 of Cu-SAPO-34 with P/Al of 0.8 dramatically decreased (220–470 °C) after hydrothermal treatment, and interestingly, the catalysts with high P/Al ratios (1.0 and 1.2) remained high activity. The T90 of the aged catalysts with P/Al of 1.2 was 155–525 °C. The characterizations showed that the increase of P/Al ratio not only enhanced the crystallinity but also enlarged the grain size of catalysts, which were conducive to the zeolite framework stability. Moreover, the Cu-SAPO-34 with large grain size facilitated the conversion of CuO to isolated Cu2+ ions as well as inhibited the aggregation of Cu species. Furthermore, the large grain sized catalysts provided more acid sites, and thus, the catalysts presented excellent hydrothermal stability. In situ DRIFTS analysis confirmed the existence of both Langmuir-Hinshelwood and Eley-Rideal pathway over the catalyst with a P/Al ratio of 1.2. This work provided a facile method to promote the hydrothermal stability of Cu-based zeolite catalysts.

Chemical Interaction Between MgO Support and Iron Catalyst

In this paper the chemical interaction between catalyst and support has been studied to understand the observed different growth rate of CNTs in our previous paper. Both pure MgO and Mg(NO3)2 . 6H2O as sources of the MgO catalyst support and Fe2(SO4)3 · xH2O as the source of the Fe catalyst, were employed. A Fe catalyst supported on MgO has been synthesized using the wet impregnation method followed by calcination. To compare the catalyst grain size and its distribution, the sample were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and BET specific surface area (SSA) measurement and X-ray photoelectron spectroscopy (XPS). XPS technique have utilized complementary to demonstrate the existence of chemical interaction between MgO support and Fe catalyst. Results revealed that the type of precursor used to prepare the support has a significant influence on the morphology of the support and the associated distribution of the Fe catalysts. The highest yield of MgFe2O4 phase was obtained using a pure MgO precursor which after calcination results in a homogenous distribution of nano-sized Fe particles over the support surface

Effect of Mo addition on the microstructure and catalytic performance Fe-Mo catalyst

Fe-Mo catalyst with different molar ratios (1:0, 1:0.5, 1:1, 1:2, 1:3) were prepared by chemical co-precipitation method, and they were added to phenolic resin as catalysts. The microstructure and physicochemical properties of catalyst and crystalline carbon after phenolic resin pyrolysis were characterized by XRD, SEM, FT-IR, XPS and TEM. The results showed that the Fe/Mo molar ratio played a significant role in the graphitization of phenolic resin and the morphology of carbon nanotubes. The graphitization of the phenolic resin first increased and then decreased with the addition of Mo. When the Fe/Mo molar ratio was 1:2, the phenolic resin achieved the highest graphitization, and the formed carbon nanotubes had the highest crystallinity. The Fe atoms were in an electron-deficient state due to the electrons transferring from Fe to Mo, which enhanced the hydrocarbon compounds absorption on the surface of catalyst. And Mo was carbonized by carbon atoms to form α-MoC1-x, and then decomposed into β-Mo2C and graphite carbon, obtaining carbon atoms orderly arrangement and carbon nanotubes. Therefore, both the grain size and electron structure of catalyst significantly affect the catalytic properties of Fe-based catalyst.

Preparation and characterization of CuO-CeO2-ZrO2/cordierite monolith catalysts

CuO-CeO2-ZrO2/cordierite catalysts have been successfully prepared by the impregnation reduction method. The effects of processing parameters such as the condition of reduction process, calcination temperature, the addition of surfactant on the size and shape of catalyst particles were studied by X-ray diffraction (XRD), BET surface area measurements, and scanning electron microscopy (SEM). The catalytic performance of the as-prepared catalysts for CO oxidation were evaluated by using a microreactor-GC system. The results indicate that the processing parameters influence greatly the size and shape of catalyst particles. Fragmental shape catalysts were formed when the impregnated samples were reduced in the thermostat water bath. However, spherical-like particles were obtained by ultrasonic-assisted in the reduction process. Tiny flower-like catalyst particles were found when the surfactant were used. When the calcination temperature decreased, the grain size of catalysts has reduced, and the catalytic activity for CO oxidation has been improved. The introduction of ultrasonic and surfactant resulted in larger specific surface area and better catalytic performance.

Effect of current stress during thermal CVD of multilayer graphene on cobalt catalytic layer

To improve the crystallinity of multilayer graphene (MLG) by CVD at a low temperature, the effect of current stress during thermal CVD on a cobalt (Co) catalytic layer was investigated. The crystallinity of MLG obtained by CVD with current was higher than that without current at the same temperature. This indicates that current has effects besides the Joule heating effect. The current effects on the Co catalytic layer and the MLG growth reaction were investigated, and it was found that current had small effects on the grain size and crystal structure of the Co catalyst and large effects on the MLG growth reaction such as large grain growth and a low activation energy of 0.49 eV, which is close to the value reported for carbon surface diffusion on Co. It is considered that the enhancement of MLG growth reaction by current leads to the improved crystallinity of MLG at a relatively low temperature.

Development of nickel–iron bimetallic catalytic layer for solid oxide fuel cells: Effect of citric acid

In this paper, Ni0.75Fe0.25 catalyst layers with different citric acid contents (molar ratio of CA to metal ions ranges from 0.1 to 1.5) were prepared using thermal decomposition method. Attention was focused on the effect of citric acid on the phase structure, surface energy and coking resistance of Ni0.75Fe0.25 catalyst for solid oxide fuel cells (SOFCs). The FeNi3 phase can be observed in all reduced catalysts, while the grain size of catalysts increases with increasing CA content. The O2-TPO profiles and Raman spectra reveal that the CA1.5 catalyst has the best coking resistance among all catalysts. In addition, the cell with the CA1.5 catalyst layer has a maximum peak power density 271 mW cm−2, when operating at 650 °C in methane. Moreover, the voltage of cell with the CA1.5 catalyst layer still remains 74% of the initial value, after operating in methane for 9 h under a current density of 600 mA cm−2 at 650 °C, which is much more stable than that of the CA-free catalyst layer (53%).

Bimetallic Gold-Palladium Supported on 5A Zeolite and their Catalytic Activity for Vinyl Acetate Synthesis

5A zeolite supported Gold-Palladium (Au-Pd) bimetallic were prepared and used in vapor phase oxidation of ethylene to synthetize vinyl acetate (VA). The chemical composition of Au-Pd/5A zeolite catalyst was analyzed by a combination of atomic absorption spectrometry (AAS). The structure of Au-Pd/5A zeolite catalyst was characterized by a scanning electron microscopy (SEM) and X-ray diffraction (XRD). The catalytic activity of the Au-Pd/5A zeolite catalyst under laboratory conditions were investigated in vinyl acetate synthesis by a kind of the fixed bed reaction device. The AAS testing showed that Au and Pd supported rate were increased up to the optimum value 91.22% and 93.91% respectively at the ratio of Au/Pd=0.87. The SEM analysis results indicated that Au-Pd alloy particles of 5A zeolite catalyst can grown up and reunited obviously through before and after reaction. The XRD analysis results showed that diffraction peak of Pd (111), Pd (200), Au (111) and Au (200) became sharp gradually with the extension of reaction time, crystalline phase composition and grain size of catalyst became bigger gradually. The results about catalytic activity of the Au-Pd/5A zeolite catalyst shown that with the increasing of the Au/Pd ratio, the space-time yield and selectivity have a best value respectively; when the ratio of Au/Pd=0.87, the space-time yield were 702g/(Lh) and the selectivity were 92.8% at the ratio of Au/Pd =1.13.

Preparation and Characterization of Palladium-Gold/4A Zeolite Catalyst

Palladium-Gold(Pd-Au)/4A zeolite catalyst was prepared by using 4A zeolite as carrier and Pd-Au as active components. The structure of Pd-Au/4A zeolite catalyst was characterized by a combination of atomic absorption spectrometry (AAS), scanning electron microscopy (SEM) and X-ray diffraction (XRD).The AAS testing showed that Pd and Au supported rate were increased up to the maximum 93.88% and 90.22% respectively at the ratio of Pd/Au=1.16. The SEM analysis results indicated that Pd-Au alloy particles of 4A zeolite catalyst can grown up and reunited obviously through before and after reaction. The XRD analysis results showed that diffraction peak of Pd(111), Pd(200), Au(111) and Au(200) became sharp gradually with the extension of reaction time, crystalline phase composition and grain size of catalyst became bigger gradually. The catalytic activity of the Pd-Au /4A zeolite catalyst was elaborated in vinyl acetate synthesis and the results showed that Pd-Au/4A zeolite catalyst has excellent catalytic activity.

Optimized Distribution and Morphology of Carbon Nanofibers for a Field Emitter Grown by Nickel and Chromium Cosputtering

To obtain a high field emission (FE) current with a low driving voltage, it is important to control and optimize carbon nanofiber (CNF) array patterns for FE. While there have been various means for controlling CNF array patterns reported over the past few decades, array patterning using lithography is the method typically used to control CNF morphology. Because lithography uses many masks and is costly, it is necessary to establish a simpler process. In this study, the grain size and distribution of catalysts with phase separation were controlled. A system which controls the morphology of small bundles of CNFs was constructed with the distance between the bundles kept constant in order to obtain a higher FE current. The Ni catalyst layer for forming the CNF morphology was separated by noncatalytic Cr grains formed by cosputtering. As a result, it was possible to control the Ni content, the grain size and synthesis density of CNFs in the alloy with a varying number of nickel pellets placed on the chromium target. This method is an epochmaking CNF patterning technique very different from lithography.

Hydrocarbon Mixtures from Waste Polymer Degradation

The degradation of waste polymers is one of the possible routes of utilization. Various cracking processes are suggested for different waste polymers, when long alkyl chains are degraded and transformed into lighter hydrocarbons. Yields of the liquid and gas reaction products can be increased and composition thereof can be modified by catalysts. Catalytic cracking of polyolefin waste polymers was studied in a batch reactor without and with Y, FAU (FCC), H-ZSM5 and natural clinoptilolite zeolite catalysts. The additives of the feed polymers did not significantly affect the yields and properties of the products but the type of the catalysts did. Both the gas and liquid yields increased with the catalyst concentration. The activity of the catalysts influenced the yields and the molecular weight of the volatile compounds. In the presence of catalysts both double bond and carbon chain isomerization were observed, but the latter was less significant than the former. The minimum temperature of cracking is lower with catalyst than without catalyst. The grain size of catalyst affects the yields, but less significantly the composition of products.

Activity of Grain Catalyst

The relation between the grain size of catalyst and reaction rate, measuring the dehydrating rate of-butanol on the various space velocity with the acidclay catalyst, which are tabulated in various sizes, was investigated.As the result of experiment (shown in Fig. 1 and 2) it was recognized that the reaction rate increases with the increase of space velocity, and with the decrease of the grain size. Also the mechanism was explained that the reaction rate was controlled by the diffusion rate of reactant into grain inside through pore, and that the space velocity affects not directly the reactant concentration of the grain inside, but its outside concentration.