Catalyst Pore Size Research Articles

Model of oxygen bubbles and performance impact in the porous transport layer of PEM water electrolysis cells

The formation, growth, and stability of oxygen bubbles inside the porous transport layer (PTL) pores of the anode of a polymer electrolyte membrane water electrolysis (PEMWE) cell was investigated by 1-dimensional mathematical modeling inside the PTL and into the flow channel. The effect of oxygen bubbles on the electrolysis overpotential has been evaluated, and the results were used to predict the effects of catalyst and PTL structures on the electrolysis cell performance. The results show how surface oxygen bubbles block active catalyst sites and decrease the electrochemically active surface area (ECSA). The effects of catalyst layer wettability, PTL wettability and pore size, and the operating conditions on the growth and detachment of bubbles from the catalyst surface were modeled. The model accounts for the growth and stability of three types of bubbles in a PEMWE cell: nucleation-driven, drag-driven, and buoyancy-driven bubbles. Nucleation-driven bubbles show the smallest overpotential: 28 mV at the reference operating conditions and PEMWE properties, compared to 35 mV for the drag-driven bubbles and 43 mV for the buoyancy-driven bubbles. Catalyst wettability is found to be the most influential material property concerning bubble overpotential for all three types of bubbles. PTL wettability and the cell pressure are the next most important factors in this regard. The modeling results can be used for improved PTL, catalyst layer, and flow field design for PEMWE cells.

CO2 hydrogenation to hydrocarbons over alumina-supported iron catalyst: Effect of support pore size

The effect of support pore size of FeK/Al2O3 catalysts on the catalytic performance in CO2 hydrogenation reaction was investigated. A total of 8 iron-based catalysts supported on alumina with different pore size were prepared by incipient wetness impregnation where the amount of Fe and K were fixed at 15 and 10wt%, respectively. N2 adsorption/desorption, XRD, TPR and PZC were used to characterize the supports and catalysts. The results show that the support pore size impacts the size of Fe2O3 particles formed in the catalyst; increasing pore size of Al2O3 supports led to increased size of Fe2O3 particles formed in the pores. Catalyst pore sizes of 7–10nm and the corresponding Fe2O3 particle sizes of 5–8nm were the most active for CO2 hydrogenation to hydrocarbons. Outside this range, larger pore size further decrease the iron dispersion and reduce the number of active sites; smaller pore size is not favorable on account of the too small Fe2O3 particle sizes and lower reducibility of the small particle.

Altering bio-oil composition by catalytic treatment of pinewood pyrolysis vapors over zeolites using an auger - packed bed integrated reactor system

Pine wood pyrolysis vapors were catalytically treated using zeolite catalysts. An auger fed reactor was used for the pine wood pyrolysis while a packed bed reactor mounted on the top of the auger reactor housed the catalyst for the treatment of pine wood pyrolytic vapors. The pyrolytic vapors produced at 450 oC were passed through zeolite catalysts maintained at 425 oC at a weight hourly space velocity (WHSV) of 12 h-1. Five zeolites, including ZSM-5, mordenite, ferrierite, zeolite-Y, and zeolite-beta (all in H form), were used to study the effect of catalyst properties such as acidity, pore size, and pore structure on catalytic cracking of pine wood pyrolysis vapors. Product bio-oils were analyzed for their chemical composition (GC-MS), water content, density, viscosity, acid value, pH, and elemental compositions. Thermogravimetric analysis (TGA) was performed to analyze the extent of coking on zeolite catalysts. Application of catalysis to biomass pyrolysis increased gas product yields at the expense of bio-oil yields. While all the zeolites deoxygenated the pyrolysis vapors, ZSM-5 was found to be most effective. The ZSM-5 catalyzed bio-oil, rich in phenolics and aromatic hydrocarbons, was less viscous, had relatively lower acid number and high pH, and possessed oxygen content nearly half that of un-catalyzed bio-oil. Bronsted acidity, pore size, and shape-selective catalysis of ZSM-5 catalyst proved to be the determining factors for its activity. TGA results implied that the pore size of catalysts highly influenced coking reactions. Regeneration of the used catalysts was successfully completed at 700 oC.

Promotional Effects of CeO2 on Stability and Activity of CaO for the Glycerolysis of Triglycerides

Glycerolysis of triglycerides (corn oil) was carried out over CeO2 promoted CaO catalysts. CeO2 was introduced into CaO via the sol–gel combustion method with citrate as the precipitator. A strong interaction between CaO and CeO2 was revealed by XRD, XPS and Raman results, which results in an increased basic strength and amounts of strong basic sites. Moreover, the lixiviation of CaO in the glycerol at high temperature, which is the key problem in the glycerolysis reaction over CaO-based catalysts, was inhibited significantly. XRD, N2 adsorption–desorption isotherms and SEM results exhibit introducing CeO2 increases the surface area, pore volume and pore size of CaO catalysts, which are beneficial to the catalytic activity. The 2CaO–1CeO2 catalyst with strong basicity and large surface area achieved over 90 % conversion after 1 h while the lixiviated Ca decreased dramatically.

Expanding Small Pore Size of the Bimodal Catalyst with Surfactant and Its Application in Slurry-phase Fischer-Tropsch Synthesis

The pore size effect on the reaction activity and hydrocarbon selectivities of Fischer-Tropsch synthesis (FTS) is investigated on the Co-based bimodal catalysts with tunable small pores and large pores, prepared by employing various surfactants, such as PEG400, PEG600 and P123. The small pore size is enlarged to 4–10 nm, higher than conventional bimodal catalysts prepared by nanoparticles from sol or solution of support precursor. The depth of small pores can also be enlarged by increasing the ZrSiO4 loading amount of the Zr−Si bimodal support, promoting dispersion of cobalt nano-crystallite. The higher cobalt reduction degree is achieved on these small pore enlarged catalysts, enhancing the activity of FTS. The P123-assisted one exhibits the highest CO conversion owing to its largest small pore size. The enlarged small pore of 5 nm prepared with PEG400 is the optimized pore size to accelerate the carbon chain growth reaction, producing more heavy hydrocarbons compared to the others.

Novel sulphated zirconia pillared clay nanoparticles as catalyst in microwave assisted conversion of citronellal

Preparation of novel sulphated zirconia pillared montmorillonite and saponite clays nanoparticles (SZ/MMT and SZ/SAP) were studied to find a highly active, economist and environment friendly catalysts in the conversion of citronellal into menthol. Sulphated zirconia pillared MMT was prepared by direct sulphation into zirconia pillared MMT, which is a new and fast technique. Comparative study also conducted by evaluating the activity of SZ/MMT with sulphated zirconia nanoparticle (SZ). Material characterisation was performed by X-ray diffraction, Brunauer–Emmett–Teller surface area analysis, scanning electron microscope and also surface acidity by mean pyridine adsorption Fourier transform infrared analysis and total acidity by butylammine titration. Catalytic activity of both SZ/MMT and SZ/SAP was observed in a reaction of citronellal conversion. The operation parameters consist of technique of reaction; tandem cyclisation–hydrogenation and catalytic hydrogen transfer mechanism were investigated. The results show that the pore size of catalyst and the presence of surface acidity affect significantly to increase the isomerisation as well as hydrogenation mechanism. The catalytic hydrogen transfer over microwave irradiation was observed as the more efficient process compared to the tandem cyclisation–hydrogenation from the selectivity of the product and also the other factor influencing the surface mechanism. In another aspect, the results clearly indicated the reusable properties of the sulphated zirconia pillared clay catalysts under varied conditions. Correlation between physicochemical characters and the reaction mechanism is discussed in this study.

Improving the accuracy of catalyst pore size distributions from mercury porosimetry using mercury thermoporometry

Mercury porosimetry is still frequently used to obtain the pore size distributions (PSDs) for porous heterogeneous catalyst pellets. However, unless the contact angle in the Washburn equation is correctly calibrated, porosimetry strictly remains only a relative technique. There is a particular potential issue for catalyst samples containing heavy metals, which may present (relatively) wetting surfaces to mercury, when the standard analysis is based upon the presumption of consistent non-wetting behaviour. Data in the literature on the impact of heavy metals on mercury intrusion is conflicting with some studies suggesting they do impact intrusion and some suggesting they do not. This study uses complementary gas sorption and mercury thermoporometry experiments that were fully serially-integrated with porosimetry to provide additional information to improve the interpretation of the basic mercury porosimetry data and validate the pore sizes obtained from it. These complementary data have been used to show that the wetting effect from heavy metals on intrusion may be confined to the smallest nanopores in the sample where the pore wall potentials begin to overlap. It has also been shown that confined mercury shows a significant advanced melting effect during thermoporometry. The thermoporometry studies revealed that the common interpretation of sharp intrusion curves and high entrapment levels in porosimetry data as implying ink-bottle pore geometries is flawed.

Morphology‐dependent electrocatalytic activity of nanostructured Pt/C particles from hybrid aerosol–colloid process

An optimum nanostructure and pore size of catalyst supports is very important in achieving high catalytic performances. In this instance, we evaluated the effects of various carbon nanostructures on the catalytic performances of carbon‐supported platinum (Pt/C) electrocatalysts experimentally and numerically. The Pt/C catalysts were prepared using a hybrid method involving the preparation of dense, hollow, and porous nanostructured carbon particle via aerosol spray pyrolysis followed by microwave‐assisted Pt deposition. Electrochemical characterization of the catalysts showed that the porous Pt/C catalyst gave the best performance; its electrochemical surface area was much higher, more than twice than those of hollow or dense Pt/C. The effects of pore size on electrocatalysis were also studied. The results showed the importance of a balance between mesopores and macropores for effective catalysis with a high charge transfer rate. A fluid flow model showed that good oxygen transport contributed to the catalytic activity. © 2015 American Institute of Chemical Engineers AIChE J, 62: 440–450, 2016

Synthesis of Copper-Based Nanostructured Catalysts on SiO2-Al2O3, SiO2-TiO2, and SiO2-ZrO2 Supports for NO Reduction.

The selective catalytic reduction of NO over a series of Cu-based catalysts supported on modified silica including SiO2-Al2O3, SiO2-TiO2, and SiO2-ZrO2 prepared via a sol-gel process and a flame spray pyrolysis (FSP) was studied. The prepared catalysts were characterized by means of TEM, XRD, XRF, TPR, and nitrogen physisorption measurement techniques, to determine particle diameter, morphology, crystallinity, phase composition, copper reducibility, surface area, and pore size of catalysts. The particles obtained from sol-gel method were almost spherical while the particles obtained from the FSP were clearly spherical and non-porous nanosized particles. The effects of Si:Al, Si:Ti, and Si:Zr molar ratio of precursor were identified as the domain for different crystalline phase of materials. It was clearly seen that a high SiO2 content inhibited the crystallization of materials. The BET surface area of catalysts obtained from sol-gel method was higher than that from the FSP and it shows that surface area increased with increasing SiO2 molar ratio due to high surface area from SiO2. The catalyst performances were tested for the selective catalytic reduction of NO with H2. It was found that the catalyst prepared over 7 wt% Cu on Si02-Al2O3 support was the most active compared with the others which converted NO as more than 70%. Moreover, the excess copper decreased the performance of NO reduction, due to the formation of CuO agglomeration covered on the porous silica as well as the alumina surface, preventing the direct contact of CO2 and AL2O3.

상온 이온성액체를 이용한 호기성 벤질 알코올 산화반응용 Pd/TiO<sub>2</sub> 촉매 제조

Pd/TiO2 catalysts for aerobic benzyl alcohol oxidation were synthesized and eight different room temperature ionic liquids were used to control the palladium properties as active sites. Pd/TiO2 particles were also calcined at 300, 400 and 500 ℃ to obtain an optimum catalyst. As the calcination temperature increased, the surface area and pore volume of catalyst de- creased, but negligible changes were observed for the pore size of catalyst. However, the structural properties of catalyst var- ied with respect to the type of ionic liquids. Under identical reaction conditions, different catalytic activities were obtained depending upon the calcination temperature and type of ionic liquids. Mostly, the catalyst calcined at 400 ℃ showed higher catalytic activity than those at other temperatures. However, the catalyst prepared with 1-octyl-3-methylimidazolium hexa- fluorophosphate and 1-octyl-3-methylimidazolium trifluoromethanesulfonate showed good catalytic performance after calcina- tion at 300 ℃. Among the catalyst, Pd/TiO2 prepared with 1-octyl-3-methylimidazolium tetrafluoroborate and calcined at 400 ℃ showed the highest catalytic activity.

Pore size effects in high-temperature Fischer–Tropsch synthesis over supported iron catalysts

This paper addresses the effect of support pore sizes on the structure and performance of iron catalysts supported by mesoporous silicas in high-temperature Fischer–Tropsch synthesis. A combination of characterization techniques showed that the size of supported iron particles was controlled by catalyst pore sizes. The larger iron particles were localized in large-pore supports.Iron carbidization with carbon monoxide resulted in preferential formation of Hägg iron carbide (χ-Fe5C2). Larger iron oxide crystallites in large-pore supports were much easier to carbidize than smaller iron oxide counterparts in small-pore supports. The catalytic performance in Fischer–Tropsch synthesis was attributed to iron carbide. Higher Fischer–Tropsch reaction rates, higher olefin, and C5+ selectivity were observed over larger pore iron catalysts. High dispersion of iron oxide in small-pore silicas was not favorable for carbon monoxide hydrogenation because of poor iron carbidization.

Effect of Catalyst Properties on Hydrocracking of Pyrolytic Lignin to Liquid Fuel in Supercritical Ethanol

The metal-acid bifunctional catalysts have been used for bio-oil upgrading and pyrolytic lignin hydrocracking. In this work, the effects of the metal-acid bifunctional catalyst properties, including acidity, pore size and supported metal on hydrocracking of pyrolytic lignin in supercritical ethanol and hydrogen were investigated at 260 °C. A series of catalysts were prepared and characterized by BET, XRD, and NH3-TPD techniques. The results showed that enhancing the acidity of the catalyst without metal can promote pyrolytic lignin polymerization to form more solid and condensation to produce more water. The pore size of microporous catalyst was smaller than mesoporous catalyst. Together with strong acidity, it caused pyrolytic lignin further hydrocrack to numerous gas. Introducing Ru into acidic catalysts promoted pyrolytic lignin hydrocracking and inhibited the polymerization and condensation, which caused the yield of pyrolytic lignin liquefaction product to increase significantly. Therefore, bifunctional catalyst with high hydrocracking activity metal Ru supported on materials with acidic sites and mesopores was imperative to get satisfactory results for the conversion of pyrolytic lignin to liquid products under supercritical conditions and hydrogen atmosphere.

One-pot synthesis of promoted porous iron-based microspheres and its Fischer–Tropsch performance

Promoter modified porous iron-based microspheres were prepared through one pot solvothermal method, and employed as catalysts during Fischer–Tropsch (FT) synthesis. Specially, a microsphere was consist of nanoparticles and pores. The effect of promoter and pore on CO conversion and on lower olefins selectivity was investigated. Fe/K and Fe/Zn displayed a high selectivity to CH4 (>0wt%), which was not desirable for their application in the FT process. Na doped Fe/Na catalyst displayed optimum catalytic performance. In particular, it showed an excellent selectivity toward C5+ (59.0wt%) while yielding a CH4 product fraction lower than 11.3wt%. Fe/Mn catalyst showed a C2-4 olefins selectivity approximately 34.1wt%, but only achieved a CO conversion of 37.4%. Furthermore, the results showed that pore size of catalysts played a key role on morphology of catalysts and on catalytic performance with time on stream.

Synthesis of Ag promoted porous Fe3O4 microspheres with tunable pore size as catalysts for Fischer–Tropsch production of lower olefins

Ag promoted porous Fe3O4 microspheres with tunable pore size were synthesized via one-pot solvothermal method and employed as catalysts for Fischer–Tropsch synthesis. The introduction of Ag played an important role in regulating the pore size of catalysts and the dispersion of Fe. Comparable to unmodified catalyst in this system, Ag promoted Fe-based catalysts displayed excellent selectivity to lower olefins, particularly for Fe–0.9Ag with smaller pore size of 1.33nm and Fe dispersion of 10.1%. The maximum selectivity to C2 through C4 olefins was 43.0wt.%, and the selectivity to CH4 was low to 14.8wt.%.

The effect of pore size or iron particle size on the formation of light olefins in Fischer–Tropsch synthesis

Smaller iron or iron carbide particle was advantageous to form more light olefins and O/P of C2–C4 was more sensitive to pore size of catalysts.

Modified precipitation processes and optimized copper content of CuO–CeO2 catalysts for water–gas shift reaction

The precipitation processes of CuO–CeO2 catalysts preparation were modified, and their optimized copper content were also studied in detail. As indicated by the experimental results, the WGS catalytic activities of the CuO–CeO2 catalysts can be ranked as: stepwise precipitation (SP) > deposition–precipitation (DP) > co-precipitation (CP), suggesting that stepwise precipitation (i.e., a modified DP) is a convenient and effective method to prepare CuO–CeO2 WGS catalysts. The optimized copper contents of CuO–CeO2–SP and CuO–CeO2–CP catalysts are 20 wt.% and 25 wt.%, respectively. Their catalytic activities can be strongly correlated with the results from XRD, XPS, Raman, N2-physisorption, N2O chemisorption and H2-TPR. For DP and SP, a certain amount of copper has substitutively incorporated into ceria lattice with multiple Ce3+ and oxygen vacancies, which is considered as one relatively strong interaction between copper and ceria support. The substitutional incorporation of copper creates larger lattice distortion, lattice defect (embodying as larger lattice cell contraction of CeO2, microstrain and Raman shift) and stronger reducibility (i.e., lower reduction temperature of H2-TPR), as a consequence, higher surface energy and catalytic activity for WGS reaction. While for CP, copper nitrate and cerium nitrate were simultaneously precipitated, resulting in the burial of many copper species in ceria supports, i.e., occupancy incorporation of isolated copper into ceria lattice vacant site, which is considered as another weak interaction between copper and ceria support. Accordingly, combined with N2O chemisorption results, it is demonstrated that surface copper species of CuO–CeO2–CP are fewer and less active than those of CuO–CeO2–DP and CuO–CeO2–SP. Lastly, there is a direct relationship between the pore volume along with most probable pore size of the as-synthesized catalysts and their corresponding catalytic activities for WGS reaction.

Comparative study on diameter distribution of single-walled carbon nanotubes using growth templates with different pore sizes: Zeolite-L, ZSM-5, and MCM-41

We report a comparative study on diameter distribution of single-walled carbon nanotubes (SWNTs) grown using nanoporous templates having different pore sizes, namely, zeolite-L, ZSM-5, and MCM-41. The change in the tube diameter based on catalytic film thickness and growth temperature was systematically investigated. We prepared very thin Fe catalyst films with nominal thicknesses of 0.5, 0.7, 1, and 2 Å, and the growth temperature was varied from 850 to 925 °C. We found that the SWNT mean diameter and size distribution width decreased with decreasing catalyst film thickness, growth temperature, and pore sizes of the templates. In addition, all SWNTs grown from the nanoporous templates have narrower diameter distribution compared to the SWNTs grown from SiO2 planar surface. The obtained results are straightforward and suggest that the template growth has potential for SWNT growth with very narrow diameter distribution.

Cathode Design of Non PGM Catalysts for Anion Exchange Membrane Fuel Cells

An anion exchange membrane fuel cell (AEMFC) using hydrazine hydrate liquid fuel has been developed1 and the concept vehicle powered by Precious Metal free Liquid Feed Fuel Cell (PMfLFC) was exhibited at the 42nd and 43rd Tokyo Motor Show. For the improvement of the AEMFCs, technological breakthrough is necessary for anion exchange membranes. Especially, it is important to overcome the counteracting relationship of high ion conductance and low fuel permeability. And also, technology to control triple-phase interface formed by catalyst and ionomer is important to improve the performance. Our approach to develop the advanced AEMFC is using anion conductive quaternized aromatic multiblock copolymers, poly(arylene ether)s (QPEs)2 and control the interface and non platinum group metal (PGM) catalysts both for anode and cathode. Even for state-of-the-art proton exchange membrane fuel cell electrode that consists of Pt catalysts and perfluorinated ionomer, triple-phase interface has not been optimized and the catalyst utilization is still insufficient. This is also the case for non PGM catalyst and anion exchange ionomer. In this paper, for the preliminary study we focus on electrode design for cathode and evaluated pore size of non PGM catalyst and distribution of catalyst in the ionomer solution. The non PGM catalysts formed meso pores (10-100nm) with the mixture of carbon materials. There are two different types of pores, one is inside of the catalyst itself and the other one is outside pores between the catalysts. Mixture of non PGM catalyst and carbon materials are increased meso pores. Oxygen reduction reaction (ORR) activity of the non-PGM catalysts was evaluated in 1M KOH aq using rotating ring disk electrode (RRDE). The Fe-N-C non-PGM catalyst showed comparable ORR performance to platinum/carbon catalyst (TEV10V60E). The half wave potentials were 0.886V and 0.849V, respectively. MEA consists of the QPE membranes and ionomers were fabricated with non-PGM catalysts and subjected to performance evaluation. The MEA performance of direct hydrazine fuel cells will be shown and discussed in the meeting.

The Performance of Gold Nanoparticles Supported on Mesoporous Zirconia for the Synthesis of Azoxybenzene

Gold nanoparticles supported on mesoporous ZrO2 were prepared and their performance for the selective reductions of nitrobenzene to azoxybenzene was investigated. It was found that azoxybenzene could be successfully synthesized over these catalysts. Furthermore, the catalytic activity of catalysts is dependent on the pore size of catalyst. The catalyst Au/ZrO2-PEG-1000 with pore size of 2.2 showed higher activity than Au/ZrO2-PEG-600 with pore size of 1.9nm.

Tuning enantioselectivity in asymmetric hydrogenation of acetophenone and its derivatives via confinement effect over free-standing mesoporous palladium network catalysts

The confinement effect on enantioselective hydrogenation of acetophenone and its derivatives over free-standing mesoporous Pd network catalysts was systematically studied. It was found for the first time that the enantiomeric excess (ee) could be effectively tuned by altering the confinement effect optimized by precise control of the topology, pore size, and lattice structure of mesoporous Pd catalysts. The double gyroid structure with proper pore size and desired lattice structure formed by KBH4 reduction provided suitable microenvironment to generate optimized confinement effect. The optimized catalyst exhibited ee of 40–73% at 273K under atmospheric pressure of H2. DFT study revealed that the major enantiomeric product could be predicted by comparing relative energies of prochiral-R and -S complexes formed by acetophenone derivatives with S-proline. The energetically favored complex led to the formation of the corresponding enantiomer in excess upon hydrogenation, and ee was found to be linearly correlated with the energy difference between prochiral-R and -S complexes.