Improved Catalyst Stability Research Articles

The Impact of La Doping on Dry Reforming Ni-Based Catalysts Loaded on FSP-Alumina

The activity of nickel-based catalysts makes them promising for the dry reforming of methane (DRM), but their implementation is limited by instability which stems from undesirable selectivity to side reactions that promote carbon formation. Cobalt can be added in the form of a bimetallic Ni–Co catalyst to improve stability although this can be at the expense of activity. Here we report the impact of lanthanum doping of an alumina support on the performance of neat Ni and bimetallic Ni–Co dry reforming catalysts with the intent of improving both stability/selectivity and activity. Direct investigation of the DRM side reactions demonstrated that introducing La to the alumina support decreased the selectivity of Ni towards the Boudouard and methane cracking reactions. This afforded Ni an enhanced resistance to catalyst coking, thereby improving catalyst stability. Monometallic Ni supported by La-doped alumina was found to be the most active catalyst for the DRM with the La addition also improving catalyst stability via suppression of the Boudouard and methane cracking reactions. The benefits of La-doping on catalyst performance were less pronounced when Co was present alongside the Ni as the La superseded the positive contribution of the Co. Characterisation of the materials illustrated La inclusion into the support was in the form of single atoms highly dispersed across the Al2O3 surface, which improved support basicity and strengthened the interactions between the Ni/Co metal and the support.

Photoelectrochemical properties of ZnS- and CdS-TiO2 nanostructured photocatalysts: Aqueous sulfidation as a smart route to improve catalyst stability

ZnS- and CdS-TiO2 hetero-nanostructures were synthesized by impregnation of polyol-made ZnS, CdS quantum dots (QDs) on the surface of TiO2 nanofibers that were grown on Ti sheets by controlled corrosion. Due to their finite size, the grafted QDs were partly oxidized, when air exposed, reducing their ability to sensitize TiO2 toward photoelectrochemical (PEC) water splitting application. We showed that a subsequent aqueous sulfidation allowed recovering the initial chemical composition of the produced catalysts improving their chemical stability and consequently their PEC properties.

Development of High Durability PtCoMn Catalyst for PEFCs

Pt/C and PtCo/C electrocatalysts are well known as highly active cathode catalysts for PEFCs (1). In the previous work, in order to exceed activity of the existing catalysts, we investigated oxygen reduction reaction (ORR) activity of PtCoX (X = Mn, Ni, Fe, Cr, Ti, Cu, Zn, Mo, V, Sn, In, Pd, Ir, Ru, Au) / high surface area carbon (HSAC, Surface area of carbon = ca. 800 m2/g) ternary alloy catalyst (2). PtCoMn / HSAC showed the highest ORR activity in all of the catalysts evaluated. The ORR activity of PtCoMn / HSAC was two times higher than that of Pt / HSAC measured in MEA. In addition, we evaluated the stability of PtCoMn / HSAC in MEA by voltage cycling test. As a result of this test, it was found that the stability of PtCoMn / HSAC was as low as the existing Pt and PtCo catalysts. To understand the mechanism of decreasing ORR activity of PtCoMn / HSAC, we investigated MEA which was used in voltage cycling test by SEM / EDX and EPMA line analysis. From results of the investigation, it was found that not only Pt but also Co and Mn in the PtCoMn catalyst dissolved during the test. It was considered that the stability of PtCoMn / HSAC would be improved by suppressing the dissolution of the metal in the PtCoMn / HSAC. In this study, in order to improve the stability of the existing PtCoMn catalysts, we tried to prepare protective layer on the catalyst. In addition, we evaluated the stability of the catalyst. Fig. 1 shows mass activities and electrochemical surface area (ECSA) of the existing PtCoMn and Improved-PtCoMn catalyst with protective layer before and after the voltage cycling test. In addition, the result of the existing Pt catalyst shows as reference. As a result of this test, ORR activity and ECSA of the existing PtCoMn catalyst decreased gradually in each test. On the other hand, ORR activity and ECSA of the Improved-PtCoMn catalyst was higher than the existing catalyst. These results suggest that protective layer on the PtCoMn catalyst has good effective for improving catalyst stability against the voltage cycling test. To understand the PtCoMn dissolution phenomenon of PtCoMn catalyst, we investigated the MEA before and after the voltage cycling test by TEM. Fig. 2 shows TEM images of cross-section of the MEA before and after the test. In the case of the existing PtCoMn catalyst, a lot of huge metal particles were observed after the test. These results suggest that Pt in the PtCoMn catalyst dissolved and turn to be Pt ions, and they were re-deposited as Pt metal particles during the test (3). In contrast, in the case of the Improved-PtCoMn catalyst, the huge metal particles were less compare to the existing catalyst. Fig. 3 shows average particle size of the existing PtCoMn catalyst and Improved-PtCoMn catalyst before and after the voltage cycling test. In the case of the existing catalyst, the average particle size was significantly increased. On the other hand, in the case of the Improved-catalyst, the growth of the catalyst particle was suppressed. These results suggest that PtCoMn dissolution was prevented by the protective layer. Therefore, the stability of the catalyst was improved. 1. K. Matsutani, K. Hayakawa, T. Tada, Precious Metal Review, 54(4), 223-232 (2010). 2. M. Ishida, K. Matsutani, ECS Trans., 64(3), 107-112 (2014). 3. M. Ishida, K. Matsutani, ECS Trans., 69(17), 651-656 (2015). Figure 1

Comment on “Efficient Conversion of Methane to Aromatics by Coupling Methylation Reaction”

Liu et al. recently reported their results on coconversion of methane and methanol at 973 K over a typical methane dehydroaromatization (MDA) catalysts, Mo/HZSM-5.1 In this work, the authors claimed that adding a small amount of methanol to a methane feed led to more than two times higher methane conversion, substantially higher xylene and toluene selectivities (i.e., combined ca. 80%, nearly an order of magnitude increase as compared to experiments without methanol), and improved catalyst stability to such an extent that no deactivation was observed during 60 h on stream. If reproducible, this result would be a significant achievement, because formation of coke in the MDA reaction has been considered inevitable hitherto. To support their experimental data, Liu et al. carried out a thermodynamic analysis, whose results were in good agreement with their experimental findings.

Palladium Nanoparticles Encaged in a Nitrogen‐Rich Porous Organic Polymer: Constructing a Promising Robust Nanoarchitecture for Catalytic Biofuel Upgrading

AbstractRobust nanoarchitectures based on surfactant‐free ultrafine Pd nanoparticles (NPs) (2.7–8.2±0.5 nm) have been developed by using the incipient wetness impregnation method with subsequent reduction of PdII species encaged in the 1,3,5‐triazine‐functionalized nitrogen‐rich porous organic polymer (POP) by employing NaBH4, HCHO, and H2 reduction routes. The Pd‐POP materials prepared by the three different synthetic methods consist of virtually identical chemical compositions but have different physical and texture properties. Strong metal–support interactions, the nanoconfinement effect of POP, and the homogeneous distribution of Pd NPs have been investigated by performing 13C cross‐polarization (CP) solid‐state magic angle spinning (MAS) NMR, FTIR, and X‐ray photoelectron spectroscopy (XPS), along with wide‐angle powder XRD, N2 physisorption, high‐resolution (HR)‐TEM, high angle annular dark field scanning transmission electron microscopy (HAADF‐STEM), and energy‐dispersive X‐ray (EDX) mapping spectroscopic studies. The resulting Pd‐POP based materials exhibit highly efficient catalytic performance with superior stability in promoting biomass refining (hydrodeoxygenation of vanillin, a typical compound of lignin‐derived bio‐oil). Outstanding catalytic performance (≈98 % conversion of vanillin with exclusive selectivity for hydrogenolysis product 2‐methoxy‐4‐methylphenol) has been achieved over the newly designed Pd‐POP catalyst under the optimized reaction conditions (140 °C, 10 bar H2 pressure), affording a turnover frequency (TOF) value of 8.51 h−1 and no significant drop in catalytic activity with desired product selectivity has been noticed for ten successive catalytic cycles, demonstrating the excellent stability and reproducibility of this catalyst system. A size‐ and location‐dependent catalytic performance for the Pd NPs with small size (1.31±0.36 and 2.71±0.25 nm) has been investigated in vanillin hydrodeoxygenation reaction with our newly designed Pd‐POP catalysts. The presence of well‐dispersed electron‐rich metallic Pd sites and highly rigid cross‐linked amine‐functionalized POP framework with high surface area is thought to be responsible for the high catalytic activity and improvement in catalyst stability.

Novel non-noble bimetallic Cu-Zn/TiO2 catalysts for selective hydrogenation of butadiene

Oxide-supported copper catalysts are active for the selective hydrogenation of polyunsaturated hydrocarbons with high selectivity to alkenes formation, but a low catalytic stability limits its application. The goal of the work was to investigate whether alloying Cu with Zn will improve catalyst stability, and whether such a non-noble bimetallic catalyst could compete with noble metal-based catalysts for this type of reaction. TiO2-supported mono-metallic Cu and Zn and bimetallic Cu-Zn (Cu/Zn atomic ratio of 1 and 3) were prepared by deposition-precipitation with urea (DPU) and deposition-precipitation at pH≈8 (DP8). Small metal nanoparticles (<2nm) with uniform particle sizes were obtained from DP8 samples, while two different particle size ranges (∼3nm and >15nm) were found in the DPU samples after calcination at 400°C and then reduction at 350°C. The bimetallic character of the nanoparticles was attested by XRD and STEM-HAADF coupled with EDS analysis, as Cu3Zn alloy was found in DPU CuZn 1:1/TO2 sample and an “intermediate” Cu-Zn alloy (Cu0.9Zn0.1) was found in DPU CuZn 3:1/TiO2 sample. UV-visible spectroscopy showed that alloying of copper with zinc inhibits the reoxidation of copper by contact with air. The catalytic results showed that alloying Cu with Zn slightly decreased the activity in butadiene selective hydrogenation, but had almost no effect on the selectivity to alkenes. The important result is that the bimetallic Cu-Zn/TiO2 catalysts displayed much higher stability under isothermal reaction than Cu/TiO2, which deactivated rapidly in the first few hours. This higher stability was ascribed to the formation of a lower amount of carbonaceous species on the bimetallic catalysts, as revealed by TGA analyses. Moreover, the DP8 Cu-Zn/TiO2 samples showed lower T100% but higher stability than the corresponding DPU samples. Surprisingly, change in the composition of the Cu-Zn alloy was observed during the catalytic reaction at 105°C, with a transition from Cu3Zn to Cu0.7Zn0.3 alloy for the DPU CuZn 1:1/TiO2 sample.

Selective degradation of organic dyes by a resin modified Fe-based metal-organic framework under visible light irradiation

Metal organic frameworks (MOFs), a new class of porous crystalline materials have attracted attention because of potential applications in environmental remediation. In this work, an Fe-based MOF, FeBTC (BTC = 1,3,5-tricarboxylic acid), was successfully modified with Amberlite IRA-200 resin to yield a novel heterogeneous photocatalyst, A@FeBTC. The modification resulted in higher photocatalytic activity than FeBTC under the same conditions. After 60 min of visible light illumination (λ ≥ 420 nm) 99% of rhodamine B was degraded. The modification lowers the zeta potential, enhancing charge-based selective adsorption and subsequent photocatalytic degradation of cationic dye pollutants. The composite also improved catalyst stability and recyclability by significantly reducing loss of iron leaching. Photoluminescence studies show that introduction of the resin reduces the recombination rate of photogenerated charge carriers thereby improving the photocatalytic activity of the composite. Finally, a plausible photocatalytic reaction mechanism is proposed.

Photo-reduction of CO2 Using a Rhenium Complex Covalently Supported on a Graphene/TiO2 Composite.

One of the promising solutions for decreasing atmospheric CO2 is artificial photosynthesis, in which CO2 can be photoconverted into solar fuels. In this study, a rhenium complex Re(PyBn)(CO)3 Cl (PyBn=1-(2-picolyl)-4-phenyl-1H-1,2,3-triazole) was covalently grafted onto the surface of reduced graphene oxide (rGO). This was further combined with TiO2 to fabricate a novel catalyst composite TiO2 -rGO-Re(PyBn)(CO)3 Cl for CO2 photo-reduction. This hybrid composite demonstrated high selectivity conversion of CO2 into CO under xenon-lamp irradiation. Compared with the unsupported homogeneous catalyst Re(PyBn)(CO)3 Cl, the covalent immobilized catalyst composite TiO2 -rGO-Re(PyBn)(CO)3 Cl enhanced the turnover number six times and significantly improved catalyst stability. During the process of CO2 photo-reduction, intermediate species with lifetimes longer than hundreds of microseconds were observed and the formation of CO products was revealed using timeresolved infrared spectroscopy. A plausible mechanism for CO2 photo-reduction by the TiO2 -rGO-Re(PyBn)(CO)3 Cl catalyst composite has been suggested. The obtained results have implications for the future design of efficient catalyst composites for CO2 photo-conversion.

A New Bioinspired Perchlorate Reduction Catalyst with Significantly Enhanced Stability via Rational Tuning of Rhenium Coordination Chemistry and Heterogeneous Reaction Pathway.

Rapid reduction of aqueous ClO4(-) to Cl(-) by H2 has been realized by a heterogeneous Re(hoz)2-Pd/C catalyst integrating Re(O)(hoz)2Cl complex (hoz = oxazolinyl-phenolato bidentate ligand) and Pd nanoparticles on carbon support, but ClOx(-) intermediates formed during reactions with concentrated ClO4(-) promote irreversible Re complex decomposition and catalyst deactivation. The original catalyst design mimics the microbial ClO4(-) reductase, which integrates Mo(MGD)2 complex (MGD = molybdopterin guanine dinucleotide) for oxygen atom transfer (OAT). Perchlorate-reducing microorganisms employ a separate enzyme, chlorite dismutase, to prevent accumulation of the destructive ClO2(-) intermediate. The structural intricacy of MGD ligand and the two-enzyme mechanism for microbial ClO4(-) reduction inspired us to improve catalyst stability by rationally tuning Re ligand structure and adding a ClOx(-) scavenger. Two new Re complexes, Re(O)(htz)2Cl and Re(O)(hoz)(htz)Cl (htz = thiazolinyl-phenolato bidentate ligand), significantly mitigate Re complex decomposition by slightly lowering the OAT activity when immobilized in Pd/C. Further stability enhancement is then obtained by switching the nanoparticles from Pd to Rh, which exhibits high reactivity with ClOx(-) intermediates and thus prevents their deactivating reaction with the Re complex. Compared to Re(hoz)2-Pd/C, the new Re(hoz)(htz)-Rh/C catalyst exhibits similar ClO4(-) reduction activity but superior stability, evidenced by a decrease of Re leaching from 37% to 0.25% and stability of surface Re speciation following the treatment of a concentrated "challenge" solution containing 1000 ppm of ClO4(-). This work demonstrates the pivotal roles of coordination chemistry control and tuning of individual catalyst components for achieving both high activity and stability in environmental catalyst applications.

Key Roles of Lewis Acid-Base Pairs on ZnxZryOz in Direct Ethanol/Acetone to Isobutene Conversion.

The effects of surface acidity on the cascade ethanol-to-isobutene conversion were studied using ZnxZryOz catalysts. The ethanol-to-isobutene reaction was found to be limited by the secondary reaction of the key intermediate, acetone, namely the acetone-to-isobutene reaction. Although the catalysts with coexisting Brønsted acidity could catalyze the rate-limiting acetone-to-isobutene reaction, the presence of Brønsted acidity is also detrimental. First, secondary isobutene isomerization is favored, producing a mixture of butene isomers. Second, undesired polymerization and coke formation prevail, leading to rapid catalyst deactivation. Most importantly, both steady-state and kinetic reaction studies as well as FTIR analysis of adsorbed acetone-d6 and D2O unambiguously showed that a highly active and selective nature of balanced Lewis acid-base pairs was masked by the coexisting Brønsted acidity in the aldolization and self-deoxygenation of acetone to isobutene. As a result, ZnxZryOz catalysts with only Lewis acid-base pairs were discovered, on which nearly a theoretical selectivity to isobutene (∼ 88.9%) was successfully achieved, which has never been reported before. Moreover, the absence of Brønsted acidity in such ZnxZryOz catalysts also eliminates the side isobutene isomerization and undesired polymerization/coke reactions, resulting in the production of high purity isobutene with significantly improved catalyst stability (<2% activity loss after 200 h time-on-stream). This work not only demonstrates a balanced Lewis acid-base pair for the highly active and selective cascade ethanol-to-isobutene reaction but also sheds light on the rational design of selective and robust acid-base catalyst for C-C coupling via aldolization reaction.

Hydrogen production and coke minimization through reforming of kerosene over bi-metallic ceria–alumina supported Ru–Ni catalysts

Steam reforming of kerosene was investigated to produce syngas as a fuel for solid-oxide fuel cells. Catalytic performances of synthesized bi-metallic Ru–Ni containing ceria–alumina supported catalysts were compared with mono-metallic catalysts containing only Ni or Ru, in the reforming reaction of kerosene. These catalysts had mesoporous structures with narrow pore size distributions. Performance of the catalyst containing 1% Ru and 15% Ni was the most stable with minimum coke and CH4 formation, as compared to the mono-metallic catalysts and bi-metallic catalysts containing less Ni. Incorporation of 1% Ru into Ni based catalysts significantly improved catalyst stability. All of the catalysts were very active, giving complete conversion of kerosene at 800°C. Increase of H2O/C ratio in the feed stream also caused more stable operation with less CH4 and CO formation. Results also proved that high hydrogen yields could be obtained by steam reforming of kerosene, producing a synthesis gas which might be used as a fuel in solid oxide fuel cells.

Phosphorous Modified ZSM-5 Zeolites: Impact on Methanol Conversion into Olefins

A promising methanol-to-propylene catalyst was designed both at the molecular scale, exhibiting low Bronsted acid site density, and at the microscopic level providing large crystals (25 µm) with few defects. The potential of giant ZSM-5 zeolites synthesized in fluoride medium in the conversion of methanol into propylene led us to investigate the replacement of harmful hydrofluoric acid by non-toxic H3PO4. P-ZSM-5 zeolites were synthesized and thoroughly characterized by XRD, SEM, FT-IR, TPD propylamine, H/D isotope exchange and XRF analyses. The catalytic performance of these acid catalysts was evaluated in the methanol-to-olefins reaction at 673 K. The presence of phosphorous in the zeolite after calcination was ascertained and induced high ethylene selectivity (up to 33 %) and improved catalyst stability with respect to fluoride-mediated zeolites.

Effect of potassium addition on a long term performance of Co–ZnO–Al2O3 catalysts in the low-temperature steam reforming of ethanol: Co-precipitation vs citrate method of catalysts synthesis

The promotion effect of potassium on Co–ZnO–Al2O3 catalysts in the steam reforming of ethanol has been studied with samples prepared by co-precipitation and citrate methods. Experimental results of catalytic activity, selectivity and coke deposition phenomena are reported. Potassium addition (1 and 2wt.%) had a significant influence on catalytic efficiency at various ethanol+water vapours streams (H2O:EtOH=21:1, 15:1, 12:1 molar ratios). It acts as a promoter improving catalyst stability, activity as well as marginalizing coke deposition on the catalyst surface. Catalysts prepared by the co-precipitation method, with smaller cobalt active phase crystallites and with potassium deposited on the catalyst surface are more stable in the steam reforming of ethanol than those with large crystallites prepared by citrate method, into which potassium was introduced together with all others components. The efficiency of the potassium promotion is higher when it is deposited on the catalyst surface with smaller cobalt active phase crystallites. The water excess equivalent to the H2O:EtOH molar ratio higher than 15:1 has been necessary for the stable SRE. Even potassium-promoted K–Co–ZnO–Al2O3 catalyst needs the ethanol–water feed with a large excess of water.

Carbon Nanotube/Zeolite Hybrid Catalysts for Glucose Conversion in Water/Oil Emulsions

The isomerization of glucose to fructose and its subsequent dehydration to hydroxymethylfurfural (HMF) have been investigated on nanohybrid catalysts that stabilize emulsions comprising aqueous and organic phases. Significant improvement in catalyst stability was observed when NaX faujasite catalysts were functionalized with multiwalled carbon nanotubes (MWCNT-NaX), with a large fraction of the initial activity and selectivity preserved after several recycles. The combination of MWCNT-NaX, containing Lewis acid sites, and MWCNT-SO3H, containing Bronsted acid sites, enables glucose isomerization and fructose dehydration at high conversion and HMF selectivity. The use of a water/oil biphasic emulsion favors the continuous separation of the HMF product into the organic phase. Furthermore, selective conversion of HMF into added-value products can be accomplished in the same emulsion by incorporating a metallic function on the amphiphilic nanohybrids in the presence of hydrogen. Depending on the metal used, di...

Activation of Mo/HZSM-5 for methane aromatization

The effect of Mo/HZSM-5 pretreatment at 973 K in inert (He), oxidizing (artificial air), and carburizing (CH4/He mixture) atmospheres on its performance in non-oxidative methane dehydroaromatization (MDA) was investigated. The effect of post-synthesis silylation on deactivation of external acid sites was also studied. Precarburization resulted in increased aromatic selectivity and improved catalyst stability. The benzene selectivity was the highest for the silylated Mo/HZSM-5 catalyst (benzene + naphthalene selectivity after 1 h on stream was close to 100%). The deactivation of precarburized zeolites was less pronounced than that of zeolites heated in air or He. During heating in air or He, larger fractions of the molybdenum oxide species diffused into the micropores than during heating in methane. Carburization of the molybdenum oxide species in the micropores during MDA resulted in the formation of molybdenum carbide particles, and these contributed to pore blocking, making the Brønsted acid sites inaccessible. The formation of molybdenum carbides during heating in methane resulted in a less mobile Mo phase. It is argued that the presence of molybdenum carbide particles in the micropores contributes to rapid catalyst deactivation, in addition to the formation of hard coke on the external surface.

Improving catalyst stability in nano-structured solar and fuel cells

Catalyst stability in nano-structured dye solar cells (DSC) and nano-composite fuel cells (NFC) is one of the most important factor that determine the lifetime of these devices. Improving catalyst stability requires strong adhesion of catalyst material on the electrode which should be chemically inert to corrosive electrolyte. In DSC, the stability of catalyst depends greatly on the catalyst deposition method. For instance, thermally platinized counter-electrodes have demonstrated long term stability at 80°C. Whereas platinum catalyst deposited through other deposition methods such as sputtering, spin coating, chemical deposition, and electrochemical deposition, have been reported to be stable only at lower temperatures. Cheaper carbon-based catalyst materials including carbon composite structures, carbon nanotubes and graphene, have demonstrated long term stability at 60°C during light soaking test. In NFCs, several degradation mechanisms have been reported for low temperature (LT), intermediate temperature (IT) and high temperature (HT) NFCs. New composite materials are rapidly developing as stable options for these types of NFCs. This work highlights the major developments in the catalyst stability in DSCs and NFCs.

The synthesis of new coke‐resistant support and its application in propane dehydrogenation to propene

AbstractBACKGROUNDZSM‐5 zeolite has been used as a common support for PtSn‐based catalyst in the propane dehydrogenation reaction. But owing to its high acidy, coke accommodation and stability of the catalyst are not satisfactory. Here, in order to improve the performance, the new hierarchical‐porous ZSM‐5 (abbreviated henceforth as ZQ) has been synthesized.RESULTSBy the introduction of hierarchical‐pores in ZQ, the pore structure was changed, the acid content was decreased, and the surface properties were promoted. These modifications to zeolite greatly improved the capacity of catalysts to accommodate coke. Moreover, the coke deposit on PtSnNa/ZQ migrated from active metal to the support. As expected, by using the catalyst PtSnNa/ZQ, the catalytic performance of propane dehydrogenation to propene and the stability of the catalyst were significantly promoted.CONCLUSIONSThe new hierarchical‐porous ZSM‐5 support (ZQ) exhibits enhanced capacity to accommodate coke, and PtSnNa/ZQ enabled better propane conversion and improved catalyst stability. © 2015 Society of Chemical Industry

Octahedral Pt2CuNi Uniform Alloy Nanoparticle Catalyst with High Activity and Promising Stability for Oxygen Reduction Reaction

Development of a highly active and stable electrocatalyst is of great significance in the oxygen reduction reaction (ORR) research. Although octahedral Pt–Ni nanoparticle catalysts have attracted much interest because of their high activity, their poor stability raises a severe issue for real applications. We achieve both outstanding ORR activity and much improved catalyst stability by preparing octahedral Pt2CuNi alloy nanoparticles with uniform element distribution, with the activity far exceeding the DOE target and the stability comparable to that of state-of-the-art Pt/C. The improved stability is attributed to uniform elemental distribution within the ternary particles, which helps with formation of intact Pt surface layers and good retention of the octahedral morphology.

Steam- and autothermal-reforming of n-butanol over Rh/ZrO2 catalyst

Steam reforming (SR) and autothermal reforming (ATR) of n-butanol was studied over 0.5wt% Rh/ZrO2 catalyst at 500, 600 and 700°C, atmospheric pressure, steam to carbon (S/C) molar ratio of 4 and oxygen to carbon (O2/C) molar ratio of 0.1. The influence of the O2/C ratio on performance was also carried out at 500°C. Catalyst performance, i.e. conversion, product distribution and short-term stability, was compared with plain ZrO2 support to derive a reaction network, including contributions of reactions in the gas phase, on the support and on Rh. At 500 and 600°C the catalyst deactivated very rapidly for WGS and hydro-isomerization reactions, slightly less rapidly for reforming and significantly slower for dehydration and dehydrogenation reactions. Increasing temperature and oxygen concentration improved catalyst stability. Rh/ZrO2 showed promising performance at 700°C with complete conversion and hydrogen yield, 70% of theoretical maximum, decreasing over 21h with not more than 8 and 1% for SR and ATR, respectively. Deactivation of the catalyst for reforming is caused by carbon deposition on and near the Rh particles. At 700°C, coke forms via gas phase reactions, while catalytic reactions on the surface mainly contribute at 500 and 600°C.

Preparation and evaluation of a highly stable palladium yttrium platinum core–shell–shell structure catalyst for oxygen reduction reactions

A core–shell–shell structure Pd–Y–Pt/C catalyst was prepared using a controlled surface reaction method. The structure was confirmed by X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray (EDX) techniques. Nano-scale yttrium was formed as a shell located as the middle layer of the catalyst. Electrochemical evaluation of the Pd–Y–Pt/C with less than 7% of Pt showed an improved performance toward oxygen reduction reaction (ORR) compared to Pt/C (20wt.% Pt). Accelerated degradation tests (ADT) indicated that the addition of Y improved catalyst stability compared to Pt/C and Pd–Pt/C core–shell catalysts under various experimental conditions. This was due to the Y middle layer created approximate half-filled metal–metal d bond between Pt (or Pd) and Y. This catalyst utilized the core–shell–shell structure to minimize the Pt usage, and Y middle shell to improve stability.