Supported PtCo Catalysts Research Articles

Highly Effective Pt-Co/ZSM-5 Catalysts with Low Pt Loading for Preferential CO Oxidation in H2-Rich Mixture

New Pt-Co catalysts of hydrogen purification from CO impurities for fuel cells were fabricated via the deposition of monodispersed 1.7 nm Pt nanoparticles using laser electrodispersion on Co-modified ZSM-5 prepared by the Co(CH3COO)2 impregnation. The structure of prepared Pt-Co zeolites was studied by low-temperature N2 sorption, TEM, EDX, and XPS methods. The comparative analysis of samples with different Pt (0.01–0.05 wt.%) and Co (2.5–4.5 wt.%) contents on zeolites with the ratio of Si/Al = 15, 28, and 40 was performed in the CO-PROX reaction in H2-rich mixture (1%CO + 1%O2 + 49%H2 + 49%He). The synergistic catalytic action of Pt and Co on zeolite surface makes it possible to completely remove CO from a mixture with hydrogen in a wide temperature range from 50 to 150 °C; the high efficiency of designed composites with low Pt loading is maintained for a long time. The enhancement of PROX performance originates from the formation of new active sites for the CO oxidation at the Pt-Co interfaces within zeolite channels and at the surface. In terms of their activity, stability, and selectivity, such composites are significantly superior to known supported Pt-Co catalysts.

Single vacancy graphene supported PtCo catalyst: A facile approach to enhance methanol first dehydrogenation

Based on the DFT, the adsorption and dehydrogenation reactions of methanol over PtCo@SV have been extensively investigated. When PtCo binary metal is adsorbed on the defect of single vacancy graphene (SV) by Co atom, its stability is obviously stronger than that of pure platinum on defect of SV. Both the H-adsorption and O-adsorption on Pt and Co sites are considered as initial reaction steps. Compared with Cu site, methanol is more likely to dehydrogenate at Pt site. Although the H-adsorption on the Pt site is weaker than the O-adsorption, the dehydrogenation by the H-adsorption path has much lower energy barrier than that by the O-adsorption path. Generally, for the H-adsorption path, the adsorption is rate determining step because of the rather low dehydrogenation barrier for the H-adsorption complex (thermodynamic control), whereas the O-adsorption path is determined by its dehydrogenation step (kinetic control). Among all the PtCo@SV investigated, PtCo-2 and PtCo-3 are found to enhance the activity of catalytic dehydrogenation by the H-adsorption path on the Pt site as compared with that on Pt2@SV, which explains why PtCo catalyst has become the focus of fuel cell research in recent years.

Comparison of Electrocatalytic Properties of PtCo/Graphene Catalysts for Ethanol, Methanol and Borohydride Oxidation

In this study the graphene supported PtCo catalyst with the Pt:Co molar ratio equal to 1:7 was fabricated by means of the rapid microwave heating method with the aim to use it in an alkaline fuel cells, using ethanol, methanol and borohydride as fuel. It was found that the PtCo/GR catalyst with an average particle size of ca. 1-3 nm was synthesized by means of microwave heating of Pt(IV) and Co(II) salts in ethylene glycol solutions. The PtCo/GR catalyst shows an enhanced activity towards the oxidation of H2 generated by catalytic hydrolysis of BH4 – and direct oxidation of BH4 – ions as well as methanol and ethanol oxidation as compared with that at the graphene supported bare Co and Pt/C catalysts. It should be noted that the electrocatalytic activity of the PtCo/GR catalyst depends on the type of fuel.

Nitrogen- and oxygen-functionalized carbon nanotubes supported Pt-based catalyst for the selective hydrogenation of cinnamaldehyde

Carbon nanotubes (CNTs) supported Pt catalysts were employed to study the influence of nitrogen- and oxygen-functionalized surface on catalytic performance in the liquid-phase hydrogenation of cinnamaldehyde. Nitrogen- and oxygen-functionalized CNTs were simply treated with the hydrothermal method using ammonia and hydrogen peroxide, respectively, and the metal catalyst was prepared using an impregnation-reduction-deposition method. Here, we studied and gave some insights into the influence of the functionalization on CNTs surface chemistry environment and Pt nanoparticles using XRD, Raman spectroscopy, TEM, XPS, and nitrogen sorption techniques. It was shown that the functionalization lead to the small size distribution of Pt particles and promoted the conversion from ca. 75% to ca. 95%. To obtain the high selectivity, transition metals, cobalt and nickel, were doped into the Pt catalyst and the 99.7% conversion with the 87.9% selectivity was achieved over the nitrogen-functionalized CNTs supported PtCo catalysts. The PtCo/N-CNTs remained high activity even at 40°C and achieved 94.2% conversion and 90.3% selectivity.

Synthesis, Characterization and Properties of the Graphene Supported Pt-Co Nanocatalysts Towards the Electro-Oxidation of Methanol

Among the different types of fuel cell technologies, direct methanol fuel cells (DMFCs) are the most suitable for mobile and portable electronic applications. The development of cost-effective, active, and stable catalysts, able to substitute Pt or allow reducing the amount of it in low temperature fuel cell anodes is still in progress. In our previous works [1, 2] it has been shown that the graphene supported platinum-cobalt catalysts prepared by means of microwave synthesis enhance electrocatalytic activity towards the oxidation of borohydride and ethanol in an alkaline medium and are promising anode materials for direct borohydride fuel cells (DBFCs) and ethanol fuel cells (DEFCs). In this study investigation of activity of the graphene supported platinum-cobalt catalysts with the different Pt:Co molar ratios, fabricated by the rapid microwave heating method, towards the electro-oxidation of methanol in an acidic medium is presented. The Pt-Co/GR catalysts with the Pt:Co molar ratios equal to 1:3, 1:6, 1:20, 1:50 and 1:60 were prepared by microwave-assisted heating of required amounts of Pt(IV), Co(II) and ethylene glycol at a temperature 170 oC for 30 min. For comparison, the graphene supported Pt catalyst was also prepared at 170 oC for 30 s. The Pt loading in the synthesized catalysts was near 0.1 mg Pt cm-2. The electrochemically active surface areas of Pt in the synthesized Pt/GR and Pt-Co/GR catalysts were determined from the cyclic voltammograms of the mentioned catalysts recorded in a deaerated 0.5 M H2SO4 solution at a sweep rate 50 mV s-1 by calculating the charge associated with hydrogen adsorption (220 µCcm-2) and are 0.7 cm2 for Pt/GR and 5.2, 2.9, 1.6, 1.0 and 0.5 cm2for the Pt-Co/GR catalysts with the Pt:Co molar ratios equal to 1:3, 1:6, 1:20, 1:50 and 1:60, respectively. Values of the electrochemically active surface areas of the investigated Pt-Co/GR catalysts are 1.4-7.5 times higher than those of the Pt/GR catalyst. Electrochemical properties of Pt-Co/GR were investigated towards the electro-oxidation of methanol in acidic medium by means of cyclic voltammetry and chronoamperometry and compared with those of the bare graphene supported Pt catalyst. It has been determined that the Pt-Co/GR catalysts with the Pt:Co molar ratios equal to 1:3, 1:6, 1:20 exhibit an enhanced electrocatalytic performance for methanol electro-oxidation as compared with that of bare graphene supported platinum catalyst. Methanol oxidation current density values are ca. 2.1-3.2 times higher at the Pt-Co/GR catalysts with the above mention Pt:Co molar ratios than those at the Pt/GR catalyst. Highest electrocatalytic activity towards the electro-oxidation of methanol in acidic medium shows the graphene supported Pt-Co catalyst with the Pt:Co molar ratios equal to 1:3 and 1:6 as compared with that of catalysts with higher Pt:Co molar ratios and Pt/GR. These results obtained show that the Pt-Co/GR catalysts with the different Pt:Co molar ratios could have promising future as catalysts for DMFC.

Investigation of Graphene Supported Platinum-Cobalt Nanocomposites as Electrocatalysts for Ethanol Oxidation

In this work graphene supported PtCo catalysts with the Pt:Co molar ratios 1:7 and 1:44 were fabricated by means of the rapid microwave heating method. The surface morphology, structure and composition of the synthesized catalysts were examined by transmission electron microscopy, X-ray diffraction and inductively coupled optical emission spectroscopy. The electrocatalytic activity of the synthesized catalysts towards the oxidation of ethanol in an alkaline medium was investigated by means of cyclic voltammetry and chrono-techniques. It has been determined that the graphene supported PtCo catalyst with a lower Pt:Co molar ratio 1:7 exhibits a higher electrocatalytic activity for the oxidation reaction of ethanol as compared with those at the graphene supported bare Pt, Co and PtCo catalysts with a higher Pt:Co molar ratio 1:44.

Investigation of Nb2O5/Graphene Supported Platinum-Cobalt Nanocomposite as Electrocatalyst for the Alkaline Alcohols Fuel Cells

In this work Nb2O5/graphene supported PtCo catalyst with the Pt:Co molar ratio equal to 1:7 was fabricated by means of the rapid microwave heating method. The transmission electron microscopy (TEM) was used to detect the shape and size of catalyst particles. Inductively coupled plasma optical emission spectroscopy (ICP-OES) was employed to characterize the composition of the synthesized catalysts. The electrocatalytic activity of the prepared catalysts towards the electro-oxidation of ethanol, methanol and ethylene glycol was investigated in an alkaline medium by means of cyclic voltammetry and chrono-techniques. It has been determined that the Nb2O5/graphene supported PtCo catalyst exhibits a higher electrocatalytic activity with respect to the electro-oxidation of all alcohols as compared to that at the commercial Pt/C catalyst.

Investigation of Nb2O5/Graphene Supported Platinum-Cobalt Nanocomposite as Electrocatalyst for the Alkaline Alcohols Fuel Cells

In the present work, niobium oxide/graphene supported PtCo catalyst with the Pt:Co molar ratio 1:7 (denoted as PtCo(1:7)Nb2O5/GR) was fabricated by means of the rapid microwave heating polyol method. The surface morphology, structure and composition of the synthesized catalyst were examined by transmission electron microscopy, X-ray diffraction and inductively coupled plasma optical emission spectroscopy. The electrocatalytic activity of the synthesized catalyst towards the oxidation of alcohols – ethanol, methanol and ethylene glycol in an alkaline medium was investigated by means of cyclic voltammetry and chronoamperometry.It has been determined that the Pt loadings was 0.285 mg Pt cm–2 in the synthesized PtCo(1:7)Nb2O5/GR catalyst. For comparison, the bare commercial Pt/C (Sigma-Aldrich) catalyst with 10% wt. Pt with the Pt loading of 0.385 mg Pt cm–2 was used. The electroactive surface areas (ESAs) of the prepared and commercial catalysts were determined from the cyclic voltammograms of PtCo(1:7)Nb2O5/GR and Pt/C catalysts recorded in a deaerated 0.5 M H2SO4 solution at a sweep rate of 50 mV s–1by calculating the charge associated with the hydrogen adsorption.According to the data of TEM analysis, the Pt nanoparticles of ca. 1-2 nm in size were successively deposited onto the surface of graphene nanosheets.It has been found that niobium oxide/graphene supported PtCo catalyst with the Pt:Co molar ratios 1:7 show an enhanced electrocatalytic activity towards the oxidation of alcohols in an alkaline medium as compared with that of 10% wt. Pt implicated commercial Pt/C catalyst. Alcohols oxidation current densities were found to be ca. 3 – 40 times higher at the PtCo(1:7)Nb2O5/GR catalyst in comparison with those at the commercial Pt/C catalyst. The prepared catalyst seem to be a promising anodic material for direct alcohols fuel cells. Acknowledgement Postdoctoral fellowship is being funded by European Union Structural Funds project ”Postdoctoral Fellowship Implementation in Lithuania”.

Graphene Supported Platinum-Cobalt Nanocomposites As Electrocatalysts for Borohydride Oxidation

In relation to other types of fuel cells direct borohydride fuel cells (DBFCs) are of particular value for their high theoretical capacity and specific energy density, i.e. 5.6 Ah/g and 9.3 Wh/g for NaBH4, respectively. For reducing the amount of Pt, transition metals such as Ni, Co, Fe, Cu have been added as alloy metals to the Pt-based catalysts. Recently, graphene as catalyst support has incurred intense interest in fuel cell applications due to its unique, outstanding physicochemical properties, such as an extremely high specific surface area (2600 m2g–1).A rapid microwave heating method was used to prepare the graphene supported PtCo catalysts with the Pt:Co molar ratio 1:7, 1:22 and 1:44. TEM and ICP-OES were employed to characterize the morphology and composition of catalysts. The electrocatalytic activity of the synthesized catalysts towards the oxidation of borohydride was investigated by means of the cyclic voltammetry and chronoamperometry. The kinetics of the catalytic hydrolysis of NaBH4 in the presence of the synthesized catalysts was also investigated.It was found that Pt nanoparticles of about 1-3 nm in size were successively deposited onto the surface of graphene nanosheets. Pt nanoparticles were uniform and well dispersed on the surface of graphene. The EDX spectra confirm the presence of Pt and Co nanoparticles in the investigated PtCo/GR catalysts.The Pt loadings were 0.125 mg Pt cm–2 in the Pt/GR and 0.165, 0.144 and 0.125 mg Pt cm–2 in the synthesized PtCo/GR having the Pt:Co molar ratio 1:7, 1:22 and 1:44, respectively. It has been determined that the synthesized graphene supported PtCo catalysts show an enhanced electrocatalytic activity towards the oxidation of H2 generated by catalytic hydrolysis of BH4 – and direct oxidation of BH4 – ions comparing with the graphene supported bare Pt and Co catalysts. The graphene supported PtCo catalyst having the Pt:Co molar ratio 1:44 exhibits the highest electrocatalytic activity for the both oxidation reactions of H2 and BH4 – ions. Acknowledgement This research was funded by a Grant (No. ATE-08/2012) from the Research Council of Lithuania.

Graphene supported platinum–cobalt nanocomposites as electrocatalysts for borohydride oxidation

In the study presented herein a rapid microwave heating method was used to prepare the graphene supported PtCo catalysts with Pt:Co molar ratio 1:7, 1:22 and 1:44. The transmission electron microscopy was employed to characterize the catalysts. Inductively coupled plasma optical emission spectrometry was used for estimation of Pt and Co metal loadings. The electrocatalytic activity of the synthesized catalysts towards the oxidation of borohydride was investigated by means of cyclic voltammetry and chronoamperometry. The kinetics of the catalytic hydrolysis of NaBH4 in the presence of the synthesized catalysts was investigated.It has been determined that the synthesized graphene supported PtCo catalysts show an enhanced electrocatalytic activity towards the oxidation of H2 generated by catalytic hydrolysis of BH4− and direct oxidation of BH4− ions comparing with the graphene supported bare Pt catalyst and graphene supported bare Co catalyst. The graphene supported PtCo catalyst having the Pt:Co molar ratio 1:44 exhibits the highest electrocatalytic activity for the both oxidation reactions of H2 and BH4− ions.

Effect of Co Loading on the Activity and Selectivity of PtCo Aqueous Phase Reforming Catalysts

The reaction site time yields (STYs, normalized to CO chemisorption sites) and product selectivity were measured for a series of bimetallic, multiwalled carbon nanotube supported PtCo catalysts with varying Pt/Co ratios for aqueous phase glycerol reforming. The STYs for all products increased by factors of around 2 for PtCo 1:0.5 and 1:1, and a factor of 4 for PtCo 1:5 relative to a monometallic Pt catalyst. The PtCo catalysts had similar hydrogen selectivity (>85%) at glycerol conversions up to 60%. X-ray absorption spectroscopy and scanning transmission electron microscopy characterization revealed that PtCo catalysts adopt monometallic Pt, mixed PtCo alloy, and Pt shell/Co core particle configurations. A linear correlation between the fraction of mixed PtCo alloy particles and the STY was found, indicating that higher Co loading resulted in a higher fraction of mixed PtCo alloy particles (the promoted phase) that provided the STY increase.

Investigation of Graphene Supported Platinum-Cobalt Nanocomposites as Electrocatalysts for Ethanol Oxidation

Graphene supported PtCo catalysts with the Pt:Co molar ratios equal to 1:1, 1:7 and 1:44 were fabricated by means of the rapid microwave heating method. A shape and size of catalyst particles were characterized using transmission electron microscopy. The structure and composition of the synthesized catalysts were examined by X-ray diffraction and inductively coupled plasma optical emission spectroscopy. The electrocatalytic activity of the synthesized catalysts toward the oxidation of ethanol in an alkaline medium was investigated by means of cyclic voltammetry and chrono-techniques. It has been determined that the graphene supported PtCo catalyst with a Pt:Co molar ratio equal to 1:7 exhibits highest electrocatalytic activity for the oxidation reaction of ethanol as compared with those at the graphene supported bare Co and PtCo catalysts with Pt:Co molar ratios equal to 1:1 and 1:44.

Oxide-supported PtCo alloy catalyst for intermediate temperature polymer electrolyte fuel cells

A Pt–Co alloy catalyst supported on a Ta-doped Ti-oxide was investigated for the oxygen reduction reaction in a polymer electrolyte fuel cell (PEMFC) operating between 80 and 110°C at different relative humidity (100% and 33% R.H.). A crystalline anatase phase was obtained for the Ta-doped Ti-oxide support with BET surface area of about 150m2/g. Pt and Pt3Co1 nanoparticles dispersed on the Ta-doped Ti-oxide showed a crystallite size of 3.9 and 2.9nm, respectively. These catalysts were investigated in PEMFC and benchmarked against a carbon supported Pt3Co1 of similar crystallite size (Pt3Co1/C). Under automotive relevant operating conditions, i.e. at intermediate temperatures (110°C), and in the presence of low relative humidity (33% R.H.), the oxide-supported PtCo was approaching in performance the Pt3Co1/C catalyst. The performance of PtCo/oxide was better than that of Pt/oxide under all operating conditions. The oxide supported PtCo catalyst showed a lower electrochemically active surface area (ECSA) and larger ohmic resistance with respect to the Pt3Co1/C. On the other hand, the oxide-supported catalysts appeared stable during an accelerated corrosion test at 1.4V RHE while a dramatic decrease of the ECSA was observed for the Pt3Co1/C under the same condition. Thus, the oxide supported PtCo alloy catalyst appears promising in terms of electrochemical stability and for automotive applications.

An electro-kinetic study of oxygen reduction in polymer electrolyte fuel cells at intermediate temperatures

The oxygen reduction process in polymer electrolyte fuel cells (PEMFCs) was in-situ investigated at intermediate temperatures (80°–130 °C) by using a carbon supported PtCo catalyst and Nafion membrane as electrolyte. To overcome the Nafion dehydration above 100 °C, the experiments were carried out under pressurized conditions. Electro-kinetic parameters such as reaction order and activation energy were determined from the steady-state galvanostatic polarization curves obtained for the PEM single cell. Negative activation energies of 40 kJ mol−1 and 18 kJ mol−1 were observed at 0.9 V and 0.65 V, respectively, in the temperature range 100°–130 °C. This was a consequence of ionomer and membrane dry-out. The ionomer dry-out effect appears to depress reaction kinetics as the temperature increases above 100 °C since the availability of protons at the catalyst–electrolyte interface is linked to the presence of proper water contents. An oxygen reduction reaction of the first order with respect to the oxygen partial pressure was determined at low current densities. Maximum power densities of 990 mW cm−2 and 780 mW cm−2 at 100 °C and 110 °C (H2–O2) with 100% R.H., were achieved at 3 bars abs.

Support effect on the low-temperature hydrogenation of benzene over PtCo bimetallic and the corresponding monometallic catalysts

PtCo bimetallic and Co, Pt monometallic catalysts supported on γ-Al2O3, SiO2, TiO2 and activated carbon (AC) were prepared and evaluated for the hydrogenation of benzene at relatively low temperatures (343K) and atmospheric pressure. Results from flow reactor studies showed that supports strongly affected the catalytic properties of different bimetallic catalysts. AC supported PtCo bimetallic catalysts exhibited significantly better performance than the other bimetallic catalysts, and all the bimetallic catalysts possessed higher activity than the corresponding monometallic catalysts. Results from CO chemisorption and H2-temperature-programmed reduction (H2-TPR) studies suggested that different catalysts possessed different properties in chemisorption capacity and reduction behavior, and AC supported PtCo catalysts possessed significantly higher CO chemisorption capacity compared to the other catalysts. Extended X-ray absorption fine structure (EXAFS) and transmission electron microscopy (TEM) analysis provided additional information regarding the formation of Pt–Co bimetallic bonds and metallic particle size distribution in the PtCo bimetallic catalysts on different supports.

Preparation of Pt-Co catalysts on mesoporous carbon and effect of alloying on catalytic activity in oxygen electro-reduction

Mesoporous carbon (MC)-supported PtCo catalysts were prepared by a sodium borohydride (NaBH4) re- duction method. To increase the alloy degree of PtCo catalyst, the heat treatment was carried out at various tem- peratures (300-700 o C). The heat-treated PtCo catalysts (PtCo/MC-x) had the higher degrees of Pt-Co alloy than that of as-synthesized PtCo catalyst (PtCo/MC). MC supported-PtCo catalyst (PtCo/MC-500) that was treated at 500 o C, had the highest activity and lowest overpotential in oxygen electro-reduction (ORR) among the prepared PtCo catalysts. The high alloy degree and favorable chemical states of PtCo/MC-500 are believed to be responsible for the superior activity in oxygen electroreduction compared to the other PtCo catalysts.

Selective hydrogenation of cinnamaldehyde to cinnamyl alcohol with carbon nanotubes supported Pt-Co catalysts

The Pt-Co catalysts supported on carbon nanotubes (CNTs) have been prepared by wet impregnation and the selective hydrogenation of cinnamaldehyde (CMA) to the corresponding cinnamyl alcohol (CMO) over the catalysts has been studied in ethanol at different reaction conditions. The results show that Pt-0.17 wt%Co/CNTs catalyst exhibits the highest activity and selectivity at a reaction temperature of 60 °C under a pressure of around 2.5 MPa, and 92.4% for the conversion of CMA and 93.6% for the selectivity of CMA to CMO, respectively. The selective hydrogenation for the C O double bond in CMA would be improved as increasing the H 2 pressure, and the selective hydrogenation for the C C double bond in CMA is enhanced as increasing the reaction temperature. In addition, these catalysts have also been characterized using transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), H 2-temperature programmed reduction (H 2-TPR) and H 2-temperature programmed desorption (H 2-TPD) techniques. The results show that Pt particles are dispersed more homogeneously on the outer surface of the nanotubes, while the strong interaction between Pt and Co would improve the increasing of activated hydrogen number because of the hydrogen spillover from reduced Pt 0 onto CNTs and increase the catalytic activity and selectivity of CMA to CMO.

Hydro-dehydrogenation of six-member hydrocarbon cycles on supported platinum–cobalt bimetallic catalysts

The dehydrogenation of cyclohexane and hydrogenation of benzene and toluene were studied on alumina- and NaY-supported Pt, Co and Pt–Co catalysts. The toluene/benzene adsorption equilibrium constant ratios were also determined. Hydro-dehydrogenation data were compared with the activities of these catalysts in CO conversion and methane 1 H– 2 H exchange data determined and published earlier for the same catalysts. Addition of Co to Pt reduced the hydro-dehydrogenation conversion rates. This effect was substantially stronger for benzene and toluene hydrogenation than that for dehydrogenation of cyclohexane. The turnover frequency (TOF) value for cyclohexane dehydrogenation indicated a synergy effect between Pt and Co in case of alumina supported Pt:Co sample of 50:50 at%. The TOF values indicated also the existence of significant “cooperation” between Pt and Co in PtCo/Al 2O 3 catalysts. Synergy, found for all samples in formation of oxygenates from CO is elucidated on the basis of Pt–Co interaction, indicated by the increased toluene/benzene adsorption equilibrium constant ratio on alumina supported PtCo catalysts. A positive correlation was observed between adsorption equilibrium constants and conversion rates of the different hydrocarbons.

Stability of Pt-Co bimetallic particles: effect of the support induced morphology on reactivity in CO hydrogenation

The structure and the stability of bimetallic particles are controlled by their interaction with surface oxide species on support or by support geometry. Location and size of the bimetallic particles estimated by XRD and XPS, depends on the environment and treatment. Thus, the Pt-Co bimetallic particles entrapped in NaY zeolite cages become unstable upon mild oxidation by O2 and/or reaction with surface protons causing the Co2+ ions formed to migrate irreversibly from the supercages into the sodalite cages as determined by TPR and TPD. Differences in the selectivity pattern observed for the CO hydrogenation over alumina and NaY zeolite supported Pt-Co catalysts, can be interpreted by the interaction between bimetallic particles with surface cobalt oxide species and the zeolite cage wall, respectively.