Loss Of Catalyst Activity Research Articles

Biodiesel production by a highly effective renewable catalyst from pyrolytic rice husk

High efficiency and stable CaO-based catalysts which used rice husk biochar as a carrier were utilized to catalyze transesterification of vegetable oil with methanol. The properties of the synthesized catalyst were determined using XRD, TGA, FT-IR, SEM, EDX, N2 adsorption/desorption, XPS and the Hammett indicator method. The influences of catalyst preparation, reaction parameters and reusability of catalyst were also investigated. The results indicated that the catalyst activity mainly depended on the pretreatment temperature, structure and basicity of the catalysts. The maximum yield could reach 93.4% under the prepared conditions of 30% CaO loading and 700 °C calcination temperature. Meanwhile, after being reused for 10 cycles, there was no noticeable loss of catalyst activity in biodiesel yield (above 85%). The appearance of CaOSi bond on the catalyst surface was the main reason for high stability. The findings suggested that the rice husk biochar based catalyst was a very promising choice for biodiesel production.

Catalytic transesterification to biodiesel at room temperature over several solid bases

The transesterification activity of several solid base catalysts in biodiesel production was systematically studied and evaluated at room temperature. Commercialized calcined silicates showed stronger transesterification ability than other commonly-used oxides, and provided considerable biodiesel yields. Biodiesel yield of >96% was obtained for Na2SiO3 catalyst (calcined at 400 °C) at 28 °C within 12 h with methanol/oil molar ratio of 12/1 and catalyst dosage of 5 wt%, and for CaSiO3 catalyst (calcined at 550 °C) at 28 °C within 24 h with methanol/oil molar ratio of 27/1 and catalyst dosage of 23 wt%. The high activity of Na2SiO3 came from low activation energy of 104.6 kJ/mol and considerable higher pre-exponential factor of 3.73 × 1015 min−1, which produced high turnover frequency of 0.234 min−1 at 28 °C. The introduction of CA-O-Si structure in CaSiO3 resulted in high surface basicity of 0.70 mmol/g and high pre-exponential factor of 3.79 × 1019 min−1 but high activation energy of 136.4 kJ/mol. The loss of catalyst activity was mainly due to the variation of surface silicate structure during transesterification.

Impact of molecular structure on the hydrogenation and oligomerization of diolefins over a Ni-Mo-S/γ-Al2O3 catalyst

The hydrogenation of a series of linear and cyclic diolefins diluted in decalin, at conditions (≤250 °C, 3.4 MPa H2 and LHSV of 1–2 h−1) chosen to mimic the hydrogenation of a Canadian oil sands naphtha (∼20 wt% olefins and 4–5 wt% diolefins) over a NiMoS/Al2O3 catalyst, is reported. The yield of dimers was minimal on fresh NiMoS/Al2O3 catalyst but increased significantly on spent NiMoS/Al2O3 catalyst recovered from a commercial hydrotreater. Dimer yield was also strongly dependent on the diolefin molecular structure. High dimer yields were obtained from molecules with conjugated double bonds, provided the double bond was not sterically hindered. Addition of 1-octene did not impact the dimer yield and 4-methylstyrene had the highest oligomer yield compared to all other diolefins examined. The results are consistent with the formation of resonance stabilized allylic carbocations being key to dimer formation. Increased concentration of the diolefin in the feed resulted in increased dimer yield and gum content of the product oil, providing a direct link between the presence of conjugated diolefins, their dimerization and gum formation that is the likely cause of catalyst activity loss and fouling of the catalyst bed.

Nanoparticle sintering in atomic layer deposition of supported catalysts: Kinetic modeling of the size distribution

In industrial catalysis, the sintering of supported nanoparticles (NPs) is often associated with the loss of catalyst activity and thus with periodic plant downtime and economic burdens. Yet, sintering mechanisms are at play also during the synthesis of the catalyst itself. They can, in fact, determine the size distribution of the NPs, and thus the activity and the stability of the catalyst. Here, we examine the role of nanoparticle sintering in a technique borrowed from the semiconductor industry that promises to reconcile atomic-scale precision with scalability: atomic layer deposition. By modeling the cyclic influx of single atoms in concomitance with NP sintering via either dynamic coalescence or Ostwald ripening, we establish the “signature” of different growth regimes: the size distribution. In contrast, we show that integral quantities such as the mean diameter, the number of NPs per unit area, and the material loading are poor indicators of the underlying growth mechanism. In particular, a constant number of NPs cannot be interpreted as a sign of no sintering. Finally, we argue that NP sintering, if properly understood, can open up new avenues for the control over the size distribution of NPs, and thus over their catalytic activity and stability.

Effect of reaction conditions on methanol to gasoline conversion over nanocrystal ZSM-5 zeolite

A nanocrystal ZSM-5 zeolite comprising uniform single crystal particles of ∼100 nm in size was synthesised and characterised using XRD, ICP–AES, SEM, TEM, solid state MAS NMR and nitrogen physisorption techniques. The catalytic performance was tested in methanol to gasoline (MTG) conversion with a particular focus on the effect of reaction conditions, namely, temperature from 300 to 450 °C, pressure from 0.1 to 2.0 MPa and WHSV from 1 to 4 h−1. Temperature showed a significant impact. At temperatures ≤350 °C, methanol conversion did not complete while the catalyst was deactivated more rapidly. Increasing temperature to above 375 °C saw complete methanol conversion and durable catalyst activity. Further increasing the reaction temperature to above 400 °C reduced gasoline yield. Pressure mainly affected the product selectivity; a higher pressure led to a lower C1–C4 selectivity but enhanced durene formation. Further increasing pressure also favoured coke formation, leading to faster loss of catalyst activity. Likewise, increasing WHSV reduced C1–C4 selectivity but promoted the formation of durene and coke, resulting in a rapid deactivation of the catalyst. The optimal reaction conditions for this nanocrystal ZSM-5 catalyst in MTG were found to be 375 °C, 1.0 MPa and WHSV of 2 h−1.

Scale and causes of catalyst activity loss in enzymatic catalyzed reactive distillation

Continuous enzymatic catalyzed reactive distillation (eRD) is a new process that can reduce product inhibition and the need for additional purification steps. However, the enzymatic catalyst is exposed to markedly different conditions than in conventional processes. The enzyme stability, a crucial cost factor, has not been investigated for the application in an eRD and the underlying mechanisms for catalyst deactivation are still unknown. This article presents for the first time a comprehensive study on the scale and causes of enzyme activity reduction in eRD processes. Pilot plant experiments with the transesterification of butyl acetate with hexanol catalyzed by Novozyme 435 confirm the existence of a process window with high reaction rates and low activity loss. The remaining activity after 320 h of operation is investigated in each reactive packing, leading to a new found cause of activity reduction that has so far not been considered for enzymatic catalyzed reactive distillation. The results allow for a better design and operation of eRD processes and the development of enzyme immobilisates that cater to the specific needs of integrated operation.

Low Temperature Selective Catalytic Reduction (SCR) of NOx Emissions by Mn-doped Cu/Al2O3 Catalysts

The 15 mol% Cu/Al2O3 catalysts with different Mn doping (0.5, 1.0, 1.5, mol%) were prepared using PEG-300 surfactant following evaporation-induced self-assembly (EISA) method. Calcination of precursors were performed in flowing air conditions at 500 ºC. The catalysts were characterized by X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscope Energy Dispersive X-Ray (SEM-EDX), Fourier Transform Infra Red (FTIR), and N2 physisorption. The catalysts activities were evaluated for H2 assisted LPG-SCR of NO in a packed bed tubular flow reactor with 200 mg catalyst under the following conditions: 500 ppm NO, 8 % O2, 1000 ppm LPG, 1 % H2 in Ar with total flow rate of 100 mL/min. Characterization of the catalysts revealed that surface area of 45.6-50.3 m2/g, narrow pore size distribution (1-2 nm), nano-size crystallites, Cu2+ and Mn2+ phases were principal active components. Hydrogen enhanced significantly selective reduction of NO to N2 with LPG over 1.0 mol % Mn-Cu/Al2O3 giving 95.56 % NO reduction at 150 ºC. It was proposed that the synergistic interaction between H2 and LPG substantially widened the NO reduction temperature window and a considerable increase in both activity and selectivity. Negligible loss of catalyst activity was observed for the 50 h of stream on run experiment at 150 ºC. The narrow pore size distribution, thermal stability of the catalyst and optimum Mn doping ensures good dispersion of Cu and Mn over Al2O3 that improved NO reduction in H2-LPG SCR system.

Buckypaper Supported Pt Monolayers Catalyst for PEM Applications

Buckypaper supported Pt monolayers catalyst for PEM applications Low temperature fuel cells such as polymer exchange membrane (PEM) or solid-acid fuel cells (SAFCs) typically utilize Pt materials as the catalyst of choice. Lowering the loading of Pt while ensuring its service life remain two major goals for lowering the cost barriers to the commercialization of these fuel cells. In addition, compacting the design of fuel cells for non-stationary applications (e.g. vehicles), while increase the output power density is a desirable achievement for a more efficient fuel cell. Conductive carbon is the current low-cost option as the catalyst support but carbon corrosion continues to be an impediment to the long-term stability of the catalyst systems in fuel cells. Carbon Nanotubes (CNT) possess high specific surface area, mechanical robustness, good tunable electrical conductivity and inertness against most of chemicals, especially acids. Over the past decade, there has been a growing interest in trying to incorporate CNT-based materials as catalyst supports especially in cases where scale-up to mass production is viable. Buckypaper, as an ultrathin mesh of aggregated CNTs can be produced in a roll-to-roll fashion for several meters, while maintaining a highly porous structure with specific surface area of hundreds meter squares per gram of CNT. In addition, their chemistry can be changed from pristine to super hydrophobic to hydrophilic through chemical functionalization of CNT. The inherent properties of CNT, its catalytic applications, high surface area and facile fabrication of buckypaper inspired us to explore the efficacy of using a few monolayers of Pt supported on buckypaper as a catalyst architecture for fuel cells. Herein, following a Surface Limited Redox Replacement (SLRR) few monolayers (MLs) of Pt are grown electrochemically on top of a stand-alone buckypaper. Pt thickness is controlled systematically through under potential deposition iterations and the growth was monitored by cyclic voltammetry (CV) scans. Pt MLs wet the CNT ribbons of the buckypaper, while avoiding agglomeration. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis show that surface-utilization is efficient, as Pt is successively deposited not only on the near surface CNTs, but down to the bulk of buckypaper. In addition, XPS analysis shows that the Pt_MLs are in their metallic state, thus confirming successful SLRR rather than eletroless deposition (where some cationic Pt would be expected). Catalyst longevity under processing conditions is a crucial factor to determine the lifetime of fuel cell and its price, which affects its commercialization directly. Department of Energy (DOE) sets a testing protocol to test catalyst activity loss under electrochemical testing. DOE protocols’ target to save 60% of the catalyst activity by 30,000 testing cycles. Our Pt_MLs/buckypaper catalysts show promising results, while saving 50% of the catalyst activity as shown through linear sweep voltammetry (LSV) currents for oxygen reduction reaction (ORR). Raman analysis shows no alteration of CNT G and 2D bands after 30,000 testing cycles, in comparison to Raman spectra of the same sample set before testing, which indicates no carbon corrosion. In conclusion, no carbon corrosion is observed for CNT after long testing (i.e. 30,000 cycles). In addition, power density of Pt MLs catalysts is enhanced by wetting-ability of Pt to the buckypaper throughout its internal 3D porous structure. Moreover, buckypaper shows high susceptibility to Pt interfacial adhesion, and the interfacial interaction between Pt and CNT surface helps to retain Pt atoms as 2D film without ripening. Catalyst activity retained after 30,000 testing cycles is ~ 50%. This initial result promises with more enhancement for power density and catalyst lifetime with chemical functionalization of CNTs in our future work.

Monitoring and Quality Control of Diesel Fraction Production Process

In this work the mathematical model of diesel fraction and atmospheric gasoil catalytic dewaxing process has been developed. Also the pattern of applying the created model to solving such problems as monitoring and quality control of diesel fraction production in the catalytic dewaxing process. It has been represented that to meet such challenges, the model should take into consideration thermodynamic and kinetic laws of hydrocarbon conversion on the catalyst surface, and instability factors that are specified by catalyst deactivation. The developed model allows controlling the quality of obtained diesel fraction depending on feed and temperature regime in the reactor. The value of model calculation absolute error does not exceed 2%, which corroborates the adequacy of the model to actual process. The computations using the model have shown that to provide the desired product yield (not less than 40% wt. of overall yield of the unit products) of programmed quality (cold filtering plugging point not higher than minus 34°C for winter diesel fuels and not lower than minus 40°C for arctic ones) at long-time catalyst operation (during 4 years), it is necessary to sustain the reactor temperature at the average level of 19°C higher than when working with fresh catalyst. This must be done to compensate catalyst activity loss due to its deactivation.

Optimization of PDMS-embedded palladium hydrodechlorination catalysts

Palladium catalysts protected by embedding in polymer films proved suitable as a means to markedly prolong the life-time of the catalyst in hydrodechlorination and hydrogenation reactions for substrates from the water phase. The present work examines and summarizes optimization strategies for synthesis of embedded Pd catalysts. The polymer and the type of Pd catalyst were varied and several synthesis strategies were compared.Poly(dimethylsiloxane) (PDMS) was confirmed to best maintaining long-term stability and offering easy surface coating with highly permeable but resistant membrane layers. The generation of catalytically active Pd species in situ within the polymer (in situ synthesis) allows higher catalyst activities due to suppression of Pd agglomeration which was omnipresent when embedding unsupported nanoparticles (ex situ synthesis). Highest Pd activities were achieved with supported porous catalysts, such as Pd on γ-Al2O3. The loss in catalyst activity due to embedding compared to freely water-suspended catalysts is less pronounced for nano-sized and supported nano-sized Pd than for micro-sized Pd. Polymer embedded Pd/Al2O3 better maintains its catalytic activity than unsupported Pd nanoparticles and Pd black. The loss of activity due to PDMS embedding is a factor of 3, 190 and 1000 respectively. Higher catalyst dispersion and Pd loadings (up to 4wt%) were obtained with condensation-vulcanizing PDMS instead of addition-vulcanizing PDMS, where the Pd load was limited due to lower Pd precursor solubility. Tailoring of the catalyst behaviour using in situ synthesized Pd-PDMS was successful by making a selection in the PDMS type, Pd loading, temperature of nanoparticle generation and type of Pd precursor.

Nb2O5/SBA-15 catalyzed propanoic acid esterification

A family of niobia (Nb2O5) functionalized SBA-15 solid catalysts have been prepared via wet impregnation with NbCl5 (2–32wt% Nb) and subsequent thermal processing, for application in the acid catalyzed esterification of propanoic acid with methanol. Bulk and surface physicochemical characterization revealed that highly dispersed niobia species present at low loadings when calcined at 500°C exhibit strong Brönsted acid character and associated activity for esterification. Increased calcination temperatures are found to result in a decrease in Brönsted:Lewis acid ratio associated with recrystallization of the niobia phase leading to a loss of catalyst activity. Esterification activity is found to be directly proportional to Brönsted:Lewis acid ratio, with the 2wt% Nb/SBA-15 catalyst pre-calcined at 500°C found to exhibit highest activity and excellent reusability without deactivation.

Graphitic Carbon Nitride as a Catalyst Support in Fuel Cells and Electrolyzers

Electrochemical power sources, such as polymer electrolyte membrane fuel cells (PEMFCs), require the use of precious metal catalysts which are deposited as nanoparticles onto supports in order to minimize their mass loading and therefore cost. State-of-the-art/commercial supports are based on forms of carbon black. However, carbon supports present disadvantages including corrosion in the operating fuel cell environment and loss of catalyst activity. Here we review recent work examining the potential of different varieties of graphitic carbon nitride (gCN) as catalyst supports, highlighting their likely benefits, as well as the challenges associated with their implementation. The performance of gCN and hybrid gCN-carbon materials as PEMFC electrodes is discussed, as well as their potential for use in alkaline systems and water electrolyzers. We illustrate the discussion with examples taken from our own recent studies.

A Metalloprotein Inspired Ruthenium Complex as an Efficient and Reusable Catalyst for Selective Oxidation of Alcohols to their Corresponding Carbonyl Compounds

AbstractMetalloprotein inspired self‐assembled ruthenium catalyst (3) was prepared from a linear amphiphilic polymer poly(N‐isopropylacrylamide‐co‐N‐vinylimidazole) (1) and ruthenium trichloride (2) via coordinative convolution. The ruthenium catalyst (3) was characterized using TEM, SEM, EDX, Powder XRD, TGA and XPS analysis. The polymer (1) was analysed using various characterization techniques such as FT‐IR, 1H and 13C NMR and GPC analysis. The prepared ruthenium catalyst (3) was highly stable, globular, highly active and reusable. The ruthenium catalyst in 863 mol ppm level (with respect to ruthenium) could catalyse the selective oxidation of various alcohol substrates efficiently within a short period of time. The catalyst could be separated by simple filtration and reused for another five consecutive runs without substantial loss in activity of catalyst or yield of product. The Turn over number (TON) and Turn over frequency (TOF) of the catalyst reached 1031 and 516 h‐1 respectively. An ICP‐AES analysis of the organic phase of the reaction revealed insignificant (0.709 ppm of Ru) leaching of the catalyst.

ChemInform Abstract: N‐Heterocyclic Carbene Coordinated Heterogeneous Pd Nanoparticles as Catalysts for Suzuki—Miyaura Coupling.

Palladium nanoparticle (Pd NP) catalysts immobilized in a polymer with an N-heterocyclic carbene (NHC) moiety (PICB-NHC-Pd) have been developed, wherein the NHC moiety plays dual roles as a crosslinker and a ligand to activate the Pd NPs. The presence of both Pd NPs and NHC was confirmed by STEM/EDS and SR-MAS NMR analyses, respectively. This PICB-NHC-Pd catalyst showed excellent activity in the Suzuki–Miyaura coupling reaction without leaching of Pd. Excellent results were obtained in gram-scale synthesis, and catalyst recovery/reuse experiments were completed without loss of catalyst activity.

Nanofibrous Electrode Design By CNT-Winded Pt/TiO2 for Superior PEMFC Performance and Durability at High Temperature

Fuel cell is one of the most promising electrochemical energy conversion devices that has many advantages such as high efficiency, high power density, CO2 free, noise free, rapid start up, etc. Especially, polymer electrolyte membrane fuel cell (PEMFC) has been shown a lot of attention due to its high power density and relatively good portability. Generally, Pt supported on carbon black is used as an electrocatalyst in PEMFC. However, carbon corrosion is one of the main problem for electrode structure collapse and catalyst activity loss, which can be further accelerated at high temperature. Therefore, we need to find an alternative catalyst support material that is electrochemically stable and interacts strongly with the catalyst active sites. Recently, metal oxide supports have been reported as promising materials due to their excellent mechanical resistance and inherently higher stability. Among many candidates, titanium dioxide (TiO2) support has an extraordinary stability under severe acidic atmosphere, which provides the possibility to directly use as a support material. However, the low electrical conductivity, catalytic activity and surface area of TiO2hinder the direct apply to the PEMFC electrode. In order to solve these problems, we prepared TiO2 nanofibers by electrospinning method and platinum nanoparticles are deposited by microwave-assisted polyol method to synthesize an effective electrode catalyst. Then, CNT was winded around the catalyst surface to boost up the electrical conductivity. Furthermore, we found a modified Pt electronic structure that takes advantage of the strong synergetic interactions of TiO2 nanofibers, Pt nanoparticles and winded-CNT. This structure influences on a decrease of the d-band vacancy of Pt due to electron transfer from the support, resulting in an improved oxygen reduction reaction. Therefore, the cathode with the CNT modified Pt/TiO2 nanofiber composite shows higher catalytic activity due to the elimination of the drawback associated with conductivity and enhanced electronic active structure. As from various PEMFC tests, our CNT-Pt/TiO2 catalyst shows superior performance and durability, which is definitely distinguishable at high temperature condition of 120 oC and RH 40% compare to the commercial Pt/C.

HC-Induced Deactivation in CO Conversion at Diesel Oxidation Catalysts

This paper examines the activity of a platinum catalyst for the oxidation of CO under conditions of temperature cycling. Each cycle consists of an ignition and extinction curve obtained with a linear temperature ramp. It is shown that the catalyst activity is higher for the first ignition cycle than for the subsequent ones regarding CO conversion. The activity for the extinction portion of each cycle is the same for all cycles. It is proposed that the loss of catalyst activity results from the deposition of hydrocarbon residues during the extinction part of the cycle. The catalyst activity can be completely restored by heating the catalyst to 350 °C in the presence of oxygen and nitrogen.

N-Heterocyclic Carbene Coordinated Heterogeneous Pd Nanoparticles as Catalysts for Suzuki–Miyaura Coupling

Palladium nanoparticle (Pd NP) catalysts immobilized in a polymer with an N-heterocyclic carbene (NHC) moiety (PICB-NHC-Pd) have been developed, wherein the NHC moiety plays dual roles as a crosslinker and a ligand to activate the Pd NPs. The presence of both Pd NPs and NHC was confirmed by STEM/EDS and SR-MAS NMR analyses, respectively. This PICB-NHC-Pd catalyst showed excellent activity in the Suzuki–Miyaura coupling reaction without leaching of Pd. Excellent results were obtained in gram-scale synthesis, and catalyst recovery/reuse experiments were completed without loss of catalyst activity.

The Flexible Design for Optimization and Debottlenecking of Multiperiod Hydrogen Networks

The operational conditions of hydrogen networks in practical refineries commonly fluctuate due to variation of feed properties, loss of catalyst activity, change of market demand, seasonal shift, and improvement of processing technology as well. These fluctuations could affect the operations of the hydrogen networks, which are usually optimized on the basis of fixed operational conditions in practice. In this work, a flexible design method of a multiperiod hydrogen network is proposed. It features the flexible design of multiperiod hydrogen network by considering discrete operational scenarios in multiple periods and possible fluctuation of each operational scenario. The optimal design of the multiperiod hydrogen network with simple structure and low total annual costs can be obtained by the proposed method. Moreover, the bottlenecks restricting the flexibility of each subperiod can also be identified and eliminated. In addition, the proposed method can be readily implemented. A multiperiod hydrogen syste...

Indium Tin Oxide as Catalyst Support for PEM Fuel Cell: RDE and MEA Performance

Introduction Conventional carbon supports suffer from catastrophic failure during start-up/shut-down events, which result in high cathode interfacial potentials, which, in turn, lead to carbon corrosion and catalyst degradation. Carbon corrosion is a major problem in fuel cells because it leads to loss of catalyst activity and collapse of electrode structure. Nissan, as an automotive OEM, has always approached the issue of catalyst support durability at the materials level, rather than at the systems-level, since system-level mitigation is an added cost to the balance of plant (BOP), and presents one additional factor that can fail during operation. NTCNA and IIT have been working on the development of high-surface-area, corrosion-resistant non-carbon supports, and we have previously demonstrated a class of highly stable non-carbon supports, e.g. ruthenium-titanium oxide (RTO) (1). In this work, we present the results of our work on a second class of non-carbon supports - tin-doped indium oxide (ITO). Materials and Methods RDE Testing – RDE tests were performed in a 3-compartment electrochemical cell containing 0.1 M HClO4 electrolyte. A glassy carbon disk (0.196 cm2) uniformly covered with Pt/C or Pt/ITO catalyst served as the working electrode. The counter and reference electrodes were Pt foil and RHE, respectively. Membrane Electrode Assembly (MEA) Fabrication - Catalyst inks were prepared by mixing Pt/C or Pt/ITO with water, n-propanol, and a Nafion ionomer dispersion. The mass-based ionomer/support (I/S) ratio in the ink was kept constant at 0.9. The cathode catalyst layers were formed on GDLs using an automated robotic spray system. MEAs (25 cm2) were prepared by hot pressing cathode GDEs (0.35 mgPt/cm2) and commercial anode GDEs (0.4 mgPt/cm2) onto Nafion® NR211 membranes. Results and Discussion Figure 1 shows the RDE performance of Pt/ITO vs. a commercially available Pt/C benchmark catalyst of comparable Pt particle size. The ECA obtained for Pt/ITO (22 m2/gPt) was lower than Pt/C (45 m2/gPt) due to the low surface area of ITO which causes Pt particle agglomeration. Even with a lower ECA, Pt/ITO shows promising performance since its mass activity of ~150 mA/mgPt matches that of the Pt/C benchmark catalyst. However, we have repeatedly observed that Pt/ITO performs very poorly in MEA testing. Figure 2 shows a typical H2/O2 polarization curve obtained for Pt/ITO at a high Pt loading of 0.35 mg/cm2. The only difference between the two MEAs is the cathode catalyst. Other than the dramatic difference between the two polarization curves, it can also be seen that Pt/ITO shows a very high HFR (high frequency resistance) of ~220 mΩ·cm2. The HFR represents the ohmic resistance due to proton transport in the membrane and the electronic contact resistances in the cell. The high HFR is attributed to the poor electronic conductivity of the ITO support since the two MEAs in Figure 2 have the same membrane, cell hardware, and cell components. It is hypothesized that hydroxylated species form on the ITO surface under fuel cell operating conditions. Hydroxide and oxy-hydroxide species may readily form on the surface of ITO due to hydrolysis reactions. Hydroxylated species such as In(OH)3 have low solubilities, hence they may remain adsorbed on the ITO surface, forming a passivating layer that will increase ohmic resistance (2). Furthermore, the Pourbaix diagram for indium shows that under fuel cell conditions, the formation of In3+ is favorable, and it is possible that In3+ can act as a poison that covers the Pt active sites. This is supported by the changes observed in the CV profile in MEA (loss of Hupd features and resistive behavior), suggesting some changes in the chemical properties of ITO and Pt poisoning. The promising RDE results did not translate to good performance in MEA, and this is hypothesized to be caused by cross-over hydrogen in MEA. H2 crossing over from anode to cathode may accelerate the formation of hydroxylated species. Experiments are underway to verify this.

Unique Chemoselective Hydrogenation using a Palladium Catalyst Immobilized on Ceramic

AbstractA heterogeneous palladium catalyst supported on a ceramic (5 % Pd/ceramic) was developed. The catalyst exhibited a specific chemoselectivity for hydrogenation that has never been achieved by other palladium‐catalyzed methods. Either aliphatic or aromatic N‐Cbz groups could be deprotected to the corresponding free‐amines, while the hydrogenolysis of benzyl esters and ethers did not proceed. Furthermore, aryl chlorides and epoxides were tolerant under the Pd/ceramic‐catalyzed hydrogenation conditions. 5 % Pd/ceramic could be reused without any loss of catalyst activity, as no palladium leaching was detected in the reaction media.