Showing papers on "Catalyst support published in 2022"

Ni-based catalysts supported on acid/alkali-activated coal fly ash residue for improved glycerol steam reforming

Abstract: Application of coal fly ash (FA) residues as catalyst support is mainly restricted because of low surface area and high sulfur content. In the present work, the physicochemical properties of a low-efficiency FA were significantly improved via simple acid/alkali treatments consisting of one-step (HNO3 or NaOH) or two-step (NaOH/HNO3 or HNO3/NaOH) leaching-partial-dissolution (LPD). As a result, as compared to Ni-FA, the catalytic activity of the Ni-FA(treated) catalysts for glycerol steam reforming was considerably enhanced. Alkali-LPD is more effective than acid-LPD in simultaneously improving FA’s surface area and regulating FA’s elemental distribution. Ni-FA(HNO3/NaOH) has the best performance with high glycerol conversion to gas (99.2%) and H2 yield (74.5%), attributed to i) removal of sulfur-containing species by acid-LPD, ii) upgrading specific surface area, iron-exposure, and Ni dispersion via alkali-LPD, iii) diminishment of coke using acid/alkali-LPD sequence treatment, and iv) enhancement of catalytic stability due to the formation of NiFe alloys.

Structure-activity relationship in hydrogenolysis of polyolefins over Ru/support catalysts

Abstract: We scrutinized the effect of supports (types and calcination temperatures) in Ru/support catalysts in the hydrogenolysis of low-density polyethylene and found that zirconia-supported Ru (Ru/ZrO2) with high-temperature (1073 K) calcined ZrO2 was an effective and reusable catalyst, showing about 3-fold higher activity on catalyst amount basis than the previously reported Ru/CeO2 catalyst with similar selectivites. The catalyst was applicable to the reactions of various polyolefins including high-density polyethylene and polypropylene. Experimental studies and catalyst characterizations such as TPR, XRD, TEM and XAS with various Ru/ZrO2 and reference catalysts such as Ru/CeO2, Ru/SiO2 and Ru/γ-Al2O3 showed good correlations between the Ru particle sizes and catalytic performance in Ru catalysts except for Ru/γ-Al2O3: The catalyst with a moderate size of ~2.5 nm Ru particles provided the highest conversion. The activity per surface Ru metal was higher at larger Ru particle sizes. The selectivity to cheap gas products was low at middle to small Ru particle sizes (1–7 nm), but high at large Ru particles (>7 nm).

Modeling the Morphological Effects of Catalyst and Ionomer Loading on Porous Carbon Supports of PEMFC

Abstract: We present a model of the cathode catalyst layer morphology before and after loading a porous catalyst support with Pt and ionomer. Support nanopores and catalyst particles within pores and on the support surface are described by size distributions, allowing for qualitative processes during the addition of a material phase to be dependent on the observed pore and particle size. A particular focus is put on the interplay of pore impregnation and blockage due to ionomer loading and the consequences for the Pt/ionomer interface, ionomer film thickness and protonic binding of particles within pores. We used the model to emulate six catalyst/support combinations from literature with different porosity, surface area and pore size distributions of the support as well as varying particle size distributions and ionomer/carbon ratios. Besides providing qualitatively and quantitatively accurate predictions, the model is able to explain why the protonically active catalyst surface area has been reported to not increase monotonically with ionomer addition for some supports, but rather decrease again when the optimum ionomer content is exceeded. The proposed model constitutes a fast translation from manufacturing parameters to catalyst layer morphology which can be incorporated into existing performance and degradation models in a straightforward way.

Nitrogen-Doped PtNi Catalysts on Polybenzimidazole-Functionalized Carbon Support for the Oxygen Reduction Reaction in Polymer Electrolyte Membrane Fuel Cells.

Abstract: PtM (M = 3d transition metals) alloys are known as the promising oxygen reduction reaction catalysts and have been considered as the replacement of pure Pt catalysts for the commercialization of proton exchange membrane fuel cells. Although great progress has been made in the past three decades, the performance and durability of PtM catalysts still face stringent challenges from practical applications. Functionalization of a catalyst carbon support with nitrogen-contained groups can add charges onto its surface, which can be utilized to build a more complete ionomer/catalyst interface, to reduce the catalyst particle size, and to improve particle size distribution. Nitriding of PtNi catalysts can effectively improve the catalyst activity and stability by the modification of lattice strain. Hereby, we propose a synergistic approach of combining polybenzimidazole-grafted Vulcan XC72 carbon as the catalyst carbon support and the nitriding of PtNi to develop PtNiN/XC72-polybenzimidazole catalysts. Such PtNiN/XC72-PBI catalysts exhibit the excellent performance of fuel cell membrane electrode assembly (i.e., mass activity, 440 mA mgPt-1; electrochemical surface area, 51 m2 gPt-1; and rated power density, 836 mW cm-2) as well as promising catalyst stability. The developed PtNiN/XC72-PBI meets the US DOE 2020 targets of mass activity for the fuel cell catalysts. This work provides a novel approach and a promising pathway on the development of the catalyst using such a synergistic approach─modification of the catalyst structure by nitrogen doping and functionalization of carbon support by polybenzimidazole for both high performance and high durability.

Fabrication of a Ceramic Foam Catalyst Using Polymer Foam Scrap via the Replica Technique for Dry Reforming

Abstract: Megapores with spherical-like cells connected through windows and high porosities make up catalyst supports in the form of ceramic foams. These characteristics provide significant benefits for catalytic processes that are limited by mass or heat transport. This study focuses on the manufacture of ceramic foam using a polymeric sponge replica process and polymer foams as a template for catalyst supports, which are industrial waste from the packaging sector. To make ceramic foam catalysts, they were dipped in a catalyst solution, followed by a breakdown stage and a sintering process. Experiments focused on determinants that affect the desired characteristics of ceramic foams, such as the types of polymer foams that affect foam morphology, the rheology of catalyst solution that affects catalyst dispersion, and the polymer decomposition rate that affects catalytic performance during dry reforming of the methane process. The cell architectures of polyurethane and polyvinyl alcohol foams are attractive for catalyst support preparation because they have 98–99% porosity and typical cell sizes of 200 and 50 μm, respectively. The polyurethane performance was superior to the performance of polyvinyl alcohol in terms of higher porosity and better catalytic-solution absorption offering high catalyst active areas. The catalyst prepared from concentrated 10 wt % Ni/Al2O3–MgO (10NAM) slurry had the highest surface area (59.18 m2/g) and the highest metal oxide dispersion (5.65%). These results are relevant to the flow behavior of catalyst slurry which plays a key role in coating the catalyst gel on the polymer template. The thermal decomposition rate used to remove the polymer template from the catalyst structure is proportional to the ceramic foam structure (catalyst support structure). The slow decomposition rate bent and fractured foam-cell struts more than the faster rate. On the other hand, achieving good catalyst dispersion on catalyst supports necessitated a high sintering rate. When sintering was adjusted at a high sintering rate, the metal–particle dispersion was relatively high, around 7.44%, and the surface area of ceramic foam catalysts was 64.61 m2/g. Finally, the catalytic behavior toward hydrogen production through the dry reforming of methane using a fixed-bed reactor was evaluated under certain operating conditions.

Effects of Spatial Distributions of Active Sites in a Silica-Supported Metallocene Catalyst on Particle Fragmentation and Reaction in Gas-Phase Ethylene Polymerization

Abstract: This work presents the experimental investigation of the effects of intraparticle catalyst site distribution on the catalyst particle fragmentation in gas-phase ethylene polymerization over a silica-supported metallocene catalyst (rac-dimethylsilylbis(2-methyl-4-phenylindenyl)-dimethyl zirconium) with methylaluminoxane (MAO) as a cocatalyst. The supported catalysts with different spatial distributions of Al and Zr were prepared by varying the catalyst immobilization conditions, and the catalyst metal distributions were analyzed using the focused ion beam (FIB) and scanning electron microscopy–energy-dispersive spectroscopy (SEM–EDX) techniques. The experimental data showed that impregnation time and catalyst solution concentration had strong effects on the radial distributions of Zr in silica particles and fines formation during the gas-phase polymerization of ethylene. The supported catalyst with a high Zr concentration near the exterior region of a catalyst particle generated more fines than a supported catalyst with uniformly distributed Zr during the gas-phase polymerization, suggesting that the optimal distribution of catalyst sites needs to be considered in designing the silica-supported catalyst for improved control of polymer particle morphology.

Synthesis and Characterization Catalyst γ-Al2O3 and Al/γ-Al2O3 Using XRD Analysis

Abstract: Catalysts have an essential role in chemical processes because they can control reactions and produce the desired product. In general, catalysts function to speed up chemical reactions that can take place by lowering the activation energy. By decreasing the activation energy, the minimum energy required for the collision is reduced so that the reaction can occur faster. Selection of the suitable material to be used as a catalyst is an effort that must be made to achieve a successful process and obtain cost efficiency. The choice of material as metal and support was the aim of this research. Aluminum (Al) was the material chosen as metal and γ-Al2O as the support. The method used in the synthesis of this catalyst was dry impregnation. It is hoped that more metal will stick to the support. In this study, catalyst synthesis was carried out with two variations of treatment. The first treatment was using Al as metal and γ-Al2O3 as the support. The second treatment did not use metal only γ-Al2O3 as the support. The resulting material was characterized by XRD analysis. The analysis found that in the diffractogram pattern of Al /γ-Al2O3, the peaks appeared at 2θ = 37o; 46o and 67o. The impregnation process went well. Aluminum was evenly distributed (sticks) to the pore surface of the support and entered the pores

High Purity Single Wall Carbon Nanotube by Oxygen-Containing Functional Group of Ferrocene-Derived Catalyst Precursor by Floating Catalyst Chemical Vapor Deposition

Abstract: Single wall carbon nanotubes (SWCNTs) were synthesized using oxygen-containing ferrocene derived catalysts. The mechanism of synthesizing carbon nanotubes was clarified by the catalyst’s exothermic or endothermic decomposition processes. By monitoring the decomposition process of ferrocene-derived catalyst precursors with and without sulfur, we found that the types of oxygen function groups closely influence catalyst formation and nanotube growth. The ferrocene-derived catalyst precursors have a different oxygen containing groups, which are hydroxyl (–OH, ferrocenenemethanol) and carbonyl (C=O, acetylferrocene, and 1,1′-diacetylferrocene). The sulfur chemical state (S 2p) on synthesized catalyst particles using acetylferrocene and 1,1′-diacetylferrocene has more sulfate (SO42−) than others, and there also is a carbon state (C-S-C). The catalyst particle using ferrocenemethanol predominant formed metal–sulfur bonds (such as S2− and Sn2−). The hydroxyl group (–OH) of ferrocenemethanol enhanced the etching effect to remove amorphous carbon and prevented oxidation on the catalyst particle surfaces; however, the carbonyl group (C=O) of acetylferrocene reacted with the catalyst particles to cause partial oxidation and carbon dissociation on the surface of the catalyst particles. The partial oxidation and carbon contamination on catalyst particles controlled the activity of the catalyst. The DFT study revealed that the ferrocene-derived catalyst precursor was dissociated according to following process: the functional groups (such as CH3CO and COH) => first Cp ligands => second Cp ligands. The pyrolysis and release of Fe ions were delayed by the functional groups of ferrocene-derived precursors compared to ferrocene. The thermal-decomposition temperature of the catalyst precursor was high, the decomposition time was be delayed, affecting the formation of catalyst particles and thus making smaller catalyst particles. The size and composition of catalyst particles not only affect the nucleation of CNTs, but also affect physical properties. Therefore, the IG/ID ratio of the CNTs changed from 74 to 18 for acetylferrocene and ferrocene, respectively. The purity also increased from 79 to 90% using ferrocene-derived precursors.

Effects of Silica Support Properties on the Performance of Immobilized Metallocene Catalysts for Ethylene Polymerization

Abstract: The choice of the silica support for α-olefin polymerization catalysts has overwhelming ramifications on the overall metal loading, catalyst performance, and properties of the resulting polymer. There are several physical properties of a silica support to consider but the pore volume and pore diameter are the two of the most important support properties in such considerations. During the catalyst immobilization process and the subsequent polymerization reaction, the change in the pore volume can either facilitate or inhibit the mass transfer of catalytic compounds and monomers within and throughout the catalyst particle. This work presents the experimental study on the effects of pore diameter and pore volume in porous silica particles used to support rac-Et(ind)2ZrCl2 catalyst on ethylene polymerization. The amount of immobilized methylaluminoxane (MAO) is varied for three commercially available silica micro-particles with similar surface areas and particle sizes. It has been observed that each type of silica exhibits different effects of the immobilized MAO on their pore characteristics, although a general trend is observed. Ethylene polymerization in slurry phase with the prepared supported catalysts also shows that the polymerization activities can be correlated with pore diameter and surface area for the three silica supports.

Building strong metal-support interactions into carbon-supported catalysts for fuel cells

Abstract: Reporting in Cell Reports Physical Science , Liang and co-workers introduced high-temperature strong metal-support interactions (SMSIs) into platinum and sulfur-doped carbon supports. The catalyst demonstrated the formation of SMSI encapsulation structures with an excellent sintering resistance (up to 1,100°C) and achieved an outstanding catalyst corrosion resistance in PEM fuel cells. Reporting in Cell Reports Physical Science , Liang and co-workers introduce high-temperature strong metal-support interactions (SMSIs) into platinum and sulfur-doped carbon supports. The catalyst demonstrated the formation of SMSI encapsulation structures with an excellent sintering resistance (up to 1,100°C) and achieved an outstanding catalyst corrosion resistance in PEM fuel cells.

Impact of catalyst support morphology on 3D electrode structure and polymer electrolyte membrane fuel cell performance

Abstract: Porous carbon-based electrodes are frequently applied in electrochemical energy technologies, for instance in fuel cells and redox flow batteries. In previous work, we observed that the final structure of a fuel cell electrode is dominated by both the morphology of the support material and its processing into a 3D porous structure. Herein, the impact of catalyst support morphology on the performance of polymer electrolyte membrane fuel cells was studied comparing carbon-supported platinum catalysts only differing in the shape of the carbon support material with otherwise similar features. Carbon-supported Pt catalysts were obtained by carbonization of polyaniline (PANI) in long fibrous, short fibrous, and granular shape. The chemical identity of the PANI precursors was demonstrated by FTIR spectroscopy and elemental analysis (EA). The final carbon-supported platinum catalysts were characterized by EA, Raman spectroscopy, XRD, and TEM exhibiting similar degree of carbonization, nanoparticle size, and nanoparticle dispersion. The effect of support morphology and the resulting differences in the 3D structure of the porous electrode were investigated by focused ion beam-scanning electron microscopy slice and view technique and correlated to their fuel cell performance.

Effect of Catalyst Support in B12-based Heterogeneous Catalysts for Catalytic Alkane Oxidations

Abstract: Heterogeneous catalysts composed of a vitamin B12 derivative with a polymer or mesoporous silica were synthesized and characterized. These two types of catalysts were used in alkane oxidation reactions with mCPBA oxidant, and improved catalytic efficiency was obtained using the polymer supported B12 catalyst with a monolith structure compared to that of the monomeric B12 catalyst. The catalytic effects were also evaluated in several alkane substrates and the polymer supported B12 catalyst showed a better performance in all reactions compared to the silica-supported B12 catalyst. Heterogeneous catalysts composed of the vitamin B12 derivative with a polymer or mesoporous silica were synthesized and characterized. These two types of catalysts were used in alkane oxidation reactions with the mCPBA oxidant, and an improved catalytic efficiency was obtained using the polymer supported B12 catalyst with the monolith structure compared to that of the monomeric B12 catalyst.

(Digital Presentation) Durable Silica Nanosheets/Carbon Black Supported Catalyst for Proton Exchange Membrane Fuel Cells

Abstract: Proton exchange membrane fuel cells (PEMFCs) which have high efficiency have attracted attention as one of the most promising energy conversion devices. Currently the catalysts in PEMFCs are mainly carbon supported noble metals where the support can afford the electron transport environment to improve catalyst efficiency and decrease catalyst loss by strengthening catalyst–support bonding [1]. Due to high electrical conductivity and surface area, carbon-based catalyst supports are widely used in PEMFCs. However, the high electric fields applied to the fuel cell can easily cause carbon corrosion and further accelerate catalyst loss. New alternative support materials are needed to reduce costs and increase the lifetime of PEMFC electrodes. Recently, silica-based supports such as silicon oxide [2, 3] and silicon carbide [4] have been considered feasible as catalyst supports due to efficient catalyst utilization and their resistance to carbon corrosion. As a silica-based material, hydrophilic silica nanosheets (SN) derived from cheap natural vermiculite [5] is for the first time to be combined with carbon black (CB) as a catalyst support in this work. SN-CB supported platinum (Pt) catalysts were prepared according to different weight ratios of SN and CB using a modified polyol reduction method [6]. After 18000-cycle accelerated stress test (AST), as shown in Fig. 1a and b, the electrochemical surface area (ECSA) of Pt/SN2-CB3 (the weight ratio of SN to CB is 2: 3) decays from 23.7 to 22.5 m2/g (only 4.8% degradation) compared to Pt/CB (25.8% degradation from 16.0 to 11.9 m2/g). Meanwhile, Pt/SN2-CB3 shows comparable initial onset potential (0.850 V) and high half-wave potential (0.654 V) compared to 0.881 V onset potential and 0.625 V half-wave potential for Pt/CB as shown in Fig. 1c and d. The half-wave potential of Pt/SN2-CB3 after AST test demonstrated the addition of SN into the support can result in a stable oxygen reduction reaction (ORR) durability. The possible reason why the ECSA, ORR activity and durability of SN-CB supported platinum catalysts are enhanced is that the synergic interactions among carbon, silica nanosheets and Pt nanoparticles may hinder carbon corrosion, Pt agglomeration and dissolution [2]. Different weight ratios between SN and CB and the functionalized SNs are currently being tested and the real fuel cell data will be presented. Reference [1] Y.-J. Wang, D.P. Wilkinson, J. Zhang, Noncarbon support materials for polymer electrolyte membrane fuel cell electrocatalysts, Chemical reviews, 111 (2011) 7625-7651. [2] P. Dhanasekaran, A. Shukla, S.V. Selvaganesh, S. Mohan, S. Bhat, Silica-decorated carbon-Pt electrocatalyst synthesis via single-step polyol method for superior polymer electrolyte fuel cell performance, durability and stack operation under low relative humidity, Journal of Power Sources, 438 (2019) 226999. [3] P. Dhanasekaran, S.V. Selvaganesh, A. Rathishkumar, S. Bhat, Designing self-humidified platinum anchored silica decorated carbon electrocatalyst for boosting the durability and performance of polymer electrolyte fuel cell stack, International Journal of Hydrogen Energy, 46 (2021) 8143-8155. [4] L. Dong, J. Zang, J. Su, Y. Jia, Y. Wang, J. Lu, X. Xu, Oxidized carbon/nano-SiC supported platinum nanoparticles as highly stable electrocatalyst for oxygen reduction reaction, International journal of hydrogen energy, 39 (2014) 16310-16317. [5] Z. Guo, J. Chen, J.J. Byun, R. Cai, M. Perez-Page, M. Sahoo, Z. Ji, S.J. Haigh, S.M. Holmes, High-performance polymer electrolyte membranes incorporated with 2D silica nanosheets in high-temperature proton exchange membrane fuel cells, Journal of Energy Chemistry, 64 (2022) 323-334. [6] Z. Ji, M. Perez-Page, J. Chen, R.G. Rodriguez, R. Cai, S.J. Haigh, S.M. Holmes, A structured catalyst support combining electrochemically exfoliated graphene oxide and carbon black for enhanced performance and durability in low-temperature hydrogen fuel cells, Energy, 226 (2021) 120318. Figure 1