Role of Mo in catalysts based on noble metals in hydrodeoxygenation reactions

The use of bio-energy as a renewable alternative to fossil fuels is nowadays attracting more and more attention. The bio-fuel from biomass seems to be a potential energy substitute for fossil fuels since it is a renewable resource that could contribute to sustainable development and global environmental preservation and it appears to have significant economic potential1. The problem is its high oxygen content, which gives undesirable properties for combustion. To remove oxygen, catalytic hydrodeoxygenation (HDO) reactions are carried out. Monometallic Mo/Si, Pt/Si as well as bimetallic PtMo/Si catalysts were prepared and evaluated in the hydrodeoxygenation (HDO)reaction of dibenzofurane (DBF) as a model molecule in biomass derived bio-oil.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Catalytic performance of bimetallic systems (Cu-Fe, Cu-Mn, Fe-Mn) based on spherical MCM-41 modified by template ion-exchange in NH3−SCRNH_{3}-SCR process

Mesoporous silica of MCM-41 type with spherical morphology was modified with copper, iron, or manganese as well as pairs of these metals by template ion-exchange (TIE) method. The obtained samples were characterized with respect to their structure (XRD), morphology (SEM-EDS), textural parameters (low-temperature N2 sorption), surface acidity (NH3-TPD), transition metal loadings (ICP-OES), their deposited forms (UV-vis DRS) and reducibility (H2-TPR). The catalytic performance of monometallic and bimetallic samples in the selective catalytic reduction of NO with ammonia (NH3-SCR) was tested. The best catalytic results presented a bimetallic copper-manganese sample, which was significantly more active than the mechanical mixture of monometallic copper and manganese catalysts. The synergistic cooperation of manganese and copper species is possibly related to charge relocation between them, resulting in activation of the catalyst in oxidation of NO to NO2, which is necessary for the fast NH3-SCR reaction

Microstructure of Bimetallic PtPd Catalysts under Oxidizing Conditions

Diesel oxidation catalysts (DOCs), which decrease the amount of harmful carbon monoxide (CO), nitrogen oxide (NO), and hydrocarbon (HC) emissions in engine exhaust, typically utilize Pt and Pd in the active phase. There is universal agreement that the addition of Pd improves both the catalytic performance and the durability of Pt catalysts. However, the mechanisms by which Pd improves the performance of Pt are less clear. Because these catalysts operate under oxidizing conditions, it is important to understand these catalysts in their working state. Herein, we report the microstructure of PtPd catalysts that are aged in air at 750 °C. After 10 h of aging, EXAFS and XANES analysis show that the Pt is fully reduced but that almost 30 % of the Pd species are present as an oxide. HRTEM images show no evidence of surface oxides on the metallic PtPd particles. Instead, the PdO is present as a separate phase that is dispersed over the alumina support. Within the metallic particles, Pt and Pd are uniformly distributed and there is no evidence of core–shell structures. Therefore, the improved catalytic performance is likely associated with the co‐existence of metallic Pt and Pd on the catalyst surface. Structured learning: A comparison of the evolution of aged and aged‐plus‐reduced Pt, Pd, and bimetallic PtPd particles is reported. The bimetallic particles grow in size and both Pt and Pd stay metallic in the form of large particles with a portion of Pd present as a dispersed Pd phase.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/99700/1/cctc_201300181_sm_miscellaneous_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/99700/2/2636_ftp.pd

Supported Co-Re Bimetallic Catalysts with Different Structures as Efficient Catalysts for Hydrogenation of Citral

International audienceBimetallic Co–Re/TiO2 catalysts were developed for efficient citral hydrogenation. Bimetallic catalysts were prepared by co‐impregnation (CI), successive‐impregnation (SI), and surface redox method (SR). The arrangement between the Co and Re species on these systems was fully characterized using several techniques (TEM–energy‐dispersive X‐ray spectroscopy, H2 temperature‐programmed reduction, temperature‐programmed desorption, XRD, CO FTIR spectroscopy, model reaction of cyclohexane dehydrogenation), and their catalytic performances were evaluated for the selective hydrogenation of citral towards unsaturated alcohols. The Re and Co species are completely isolated in the CI sample, presenting a very limited Co–Re interaction. In SI samples, the metals coexist in a Janus‐type structure with a concentration of Re around Co. Decoration/core–shell structures are observed for SR samples resulting from the redox exchange between the metallic surface of the parent Co/TiO2 catalyst and the Re7+ species of the modifier precursor salt. The contact degree between the two metals gradually increases as follows: Isolated structure (CI)<Janus‐type structure(SI)<decoration/core–shell structure (SR). The unchanging structure of all SI samples independent of the Re loading leads to similar electron transfer, and the increase in Re content results in agglomeration of Re, thus decreasing the catalytic activity. Density‐of‐state (DOS) calculations prove that the high valence of Re is a disadvantage for the hydrogenation reaction. For SR samples, the increase of Re loading contributes to the electron transfer from Re to Co that is consistent with a change of structure from decoration to core–shell. The lack of directly accessible Co atoms for SR catalysts with fully coated structure decreases the efficiency of Re reduction. The presence of Co–Re interaction resulting from the close contact between metals plays a dominant role in the hydrogenation of citral. Nevertheless, an excessively high contact degree is unnecessary for citral hydrogenation once Co–Re interaction has formed

Preparación de catalizadores de carbón activado estructurados. Un caso de estudio : síntesis limpia de dimetil carbonato a partir de metanol y CO2

RESUMEN: Se presenta la síntesis del catalizador bimetálico de Cu-Ni soportado en pellets de carbón activado utilizando carboximetilcelulosa (CMC) como agente aglutinante. Se evaluó el efecto de las condiciones de preparación, tales como concentración de CMC, relación de CMC/Carbón activado, temperatura y velocidad de calentamiento en la pirólisis sobre el área la superficial de los pellets sintetizados. La incorporación de los metales (Cu y Ni) en los pellets se efectuó por impregnación húmeda incipiente convencional. El soporte y los catalizadores sintetizados se caracterizaron mediante adsorción de N2 , H2 -TPR, XRD y técnicas de SEM-EDS. Los catalizadores peletizados se evaluaron en la síntesis directa de dimetil carbonato DMC (caso de estudio), mostrando una actividad catalítica mejorada en comparación con el catalizador en polvo.ABSTRACT: The synthesis of Cu-Ni bimetallic catalyst supported on pellets of activated carbon using carboxymethylcellulose (CMC) as a binder is reported. The effect of preparation conditions, such as binder concentration, AC/binder ratio, temperature, and pyrolysis heating rate on the surface area of the pellets, was evaluated. Cu and Ni metals were incorporated on the pellets by conventional incipient wetness impregnation. The support and the synthesized catalysts were characterized using N2 adsorption, H2-TPR, XRD and SEM-EDS techniques. The pelletized catalysts were evaluated for the direct synthesis of dimethyl carbonate DMC (case study). An improved catalytic activity (e.g., ca. 20% increase in conversion) in structured pelletized catalyst in comparison to the powdered catalyst was found

Beneficial effects of nickel promoter on the efficiency of alumina-supported Co3O4 catalysts for lean methane oxidation

In this work bimetallic Ni catalysts supported over Co-Al2O3 and monometallic Co-Al2O3 and Ni-Al2O3 catalysts were examined for the complete oxidation of methane. With a 30 % total metallic loading, the samples were synthesized by a sequential precipitation route. All samples were characterized by nitrogen physisorption, X-ray fluorescence, X-ray diffraction, Raman spectroscopy, scanning electron microscopy, scanning-transmission electron microscopy, X-Ray photoelectron spectroscopy, and temperature-programmed reduction with hydrogen and methane. Their catalytic performance was investigated in the temperature range of 200-600 degrees C with a space velocity of 60.000 h-1. The bimetallic catalysts showed a better behavior in the oxidation reaction than the monometallic counterparts, mainly due to the good dispersion of Ni on the surface of the Co-Al2O3 samples. This has enabled the insertion of Ni2+ ions into the cobalt spinel lattice, which in turn provoked an increase in the amount of Co3+ species, and a subsequent enhanced mobility of oxygen species in the spinel. In this sense, the 5Ni/25Co catalyst showed the best performance, thus reducing the value of the T50 by 25 degrees C with respect to the monometallic catalysts.This research was funded by the Spanish Ministry of Science and Innovation (PID2019-107105RB-I00 AEI/FEDER, UE), Basque Government (IT1509-22) and the University of The Basque Country UPV/EHU (DOCREC21/23). The authors wish to thank the technical and human support provided by SGIker (UPV/EHU). In addition, authors acknowledge the use of instrumentation as well as the technical advice provided by the National Facility ELECMI ICTS, node ‘Advanced Microscopy Laboratory’ at University of Zaragoza

Carbon supported bimetallic Ru‐Co catalysts for H2 production through NaBH4 and NH3BH3 hydrolysis

Summary This work investigates the effect of the addition of small amounts of Ru (0.5-1 wt%) to carbon supported Co (10 wt%) catalysts towards both NaBH4 and NH3BH3 hydrolysis for H2 production. In the sodium borohydride hydrolysis, the activity of Ru-Co/carbon catalysts was sensibly higher than the sum of the activities of corresponding monometallic samples, whereas for the ammonia borane hydrolysis, the positive effect of Ru-Co systems with regard to catalytic activity was less evident. The performances of Ru-Co bimetallic catalysts correlated with the occurrence of an interaction between Ru and Co species resulting in the formation of smaller ruthenium and cobalt oxide particles with a more homogeneous dispersion on the carbon support. It was proposed that Ru°, formed during the reduction step of the Ru-Co catalysts, favors the H2 activation, thus enhancing the reduction degree of the cobalt precursor and the number of Co nucleation centers. A subsequent reduction of cobalt and ruthenium species also occurs in the hydride reaction medium, and therefore the state of the catalyst before the catalytic experiment determines the state of the active phase formed in situ. The different relative reactivity of the Ru and Co active species towards the two investigated reactions accounted for the different behavior towards NaBH4 and NH3BH3 hydrolysis

Adatom Emission From Nanoparticles: Implications for Ostwald Ripening

To achieve clean air in our cities, all modern means of ground transportation make use of catalytic converters. Precious metal-based catalysts such as Pt and Pd are currently used in catalytic converters. To achieve higher fuel efficiency, combustion can be carried out in excess air resulting in a reduction of greenhouse gas (GHG) emissions. Reduction of these emissions has emerged as a major challenge. Most of the pollutants are emitted within the first 30 seconds after starting an engine because the catalyst is cold. The development of catalysts which achieve high activity at low temperatures will improve fuel efficiency and therefore reduce the nations dependence on foreign fossil fuels. The supplies of precious metals are limited worldwide, but there is increasing demand for clean energy. Therefore, there is a need to develop more active catalysts that provide long-term stable performance at elevated temperatures with minimal use of precious metals such as platinum. A major problem is that catalysts lose activity during use. Pt particles sinter, leading to poor stability. There is universal agreement that addition of Pd improves the catalytic performance as well as the durability of the Pt catalysts; however, the mechanisms by which Pd improves the performance of Pt are less clear. Conventional supported catalysts (Pt, Pd, and Pt-Pd) have been used to explore the microstructure of diesel oxidation catalysts (DOCs) in their working state (i.e. under oxidizing conditions). Model catalysts have been used to study the evolution of platinum and palladium nanoparticles. Both a statistical and a microscopic approach have been used to understand the ways in which Pd affects Pt. The catalytic activity and kinetics of various monometallic as well as bimetallic powder catalysts aged under different conditions has also been studied. NO oxidation in the presence of NO, O2, and NO2 was the probe reaction used to distinguish between the differing activities of Pt/Al2O3 and Pt-Pd/Al2O3. The work described here focuses on important problems in the field of catalysis. A fundamental understanding of the role of palladium on both the catalytic activity and long-term performance of platinum catalysts has been gained.\u2

Bimetallic NiFe nanoparticles supported on CeO2 as catalysts for methane steam reforming

Ni-Fe nanocatalysts supported on CeO2 have been prepared for the catalysis of methane steam reforming (MSR) aiming for coke-resistant noble metal-free catalysts. The catalysts have been synthesized by traditional incipient wetness impregnation as well as dry ball milling, a green and more sustainable preparation method. The impact of the synthesis method on the catalytic performance and the catalysts’ nanostructure has been investigated. The influence of Fe addition has been addressed as well. The reducibility and the electronic and crystalline structure of Ni and Ni-Fe mono- and bimetallic catalysts have been characterized by temperature programmed reduction (H2-TPR), in situ synchrotron X-ray diffraction (SXRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Their catalytic activity was tested between 700 and 950 °C at 108 L gcat-1 h-1 and with the reactant flow varying between 54 and 415 L gcat-1 h-1 at 700 °C. Hydrogen production rates of 67 mol gmet-1 h-1 have been achieved. The performance of the ball-milled Fe0.1Ni0.9/CeO2 catalyst was similar to that of Ni/CeO2 at high temperatures, but Raman spectroscopy revealed a higher amount of highly defective carbon on the surface of Ni-Fe nanocatalysts. The reorganization of the surface under MSR of the ball-milled NiFe/CeO2 has been monitored by in situ near-ambient pressure XPS experiments, where a strong reorganization of the Ni-Fe nanoparticles with segregation of Fe toward the surface has been observed. Despite the catalytic activity being lower in the low-temperature regime, Fe addition for the milled nanocatalyst increased the coke resistance and could be an efficient alternative to industrial Ni/Al2O3 catalysts.Peer ReviewedPostprint (published version

Palladium-platinum powder catalysts manufactured by colloid synthesis II. Characterization and catalytic tests after oxidizing and reducing treatment

Unsupported Pd, Pt and PdPt bimetallic catalysts were prepared in different atomic ratios using methods of colloid chemistry. They were characterized by XPS, UPS and TEM. Four subsequent treatments with O2 and H2 up to T = 603K were applied in the preparation chamber of the electron spectrometer and before the catalytic runs. Platinum strongly hindered the oxidation of palladium in the bimetallic samples indicating an alloying of the two components. The H2 treatment after O2 led to rather clean metals. These treatments up to 603K decreased the Pt enrichment near to the surface found by XPS, destroying presumably the Pt islands on the surface of a Pd-rich matrix. The particle composition approached thus a homogeneous metal mixture. The catalytic behavior was tested in the hydrogenative ring opening reaction of cis- and trans-methyl-ethyl-cyclopropane (MECP) at 373 K. The product ratios 2-methylpentane/3-methylpentane (2MP/3MP) and 2-methylpentane/n-hexane (2MP/nH) were used to characterize the ring-opening pattern of the samples. The bimetallic catalysts revealed higher activity and completely different selectivities than the monometallic Pt and Pd. Moreover, the 2MP/3MP ratio from trans-MECP and 2MP/nH ratio from cis-MECP increased as the surface Pt enrichment decreased. PdPt catalysts were cleaner than Pd or Pt, their activity higher and selectivity closer to random C C rupture, due, very likely, to the presence of active Pd-Pt ensembles