Über Mischsalzkontakte. XV. Selektive Hydrierung von Cyclopropan und Propen an Nickelkontakten. II

Langenbeck, Wolfgang; Dreyer, H.; Fuhrmann, Hans

doi:10.1002/zaac.19623140307

Cited by 12 publications

(2 citation statements)

References 11 publications

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“…The alternative change of hot electron generation (red line) is consistent with the accumulation cycles of the produced CO 2 (black line). Notably, our detection of hot electron current from catalytic nanodiodes is consistent with the early argument given by Schwab [29,30], Solymosi [31], and Langenbeck et al [32]. They suggested the importance of electron flow at oxide-metal interfaces for several catalysis reactions including CO oxidation, SO 2 oxidation, formic acid decomposition, ethylene hydrogenation, cyclohexene hydrogenation and dehydrogenation, and ammonia synthesis [31,33].…”

Section: Oxide-metal Interfacesupporting

confidence: 89%

The Nanoscience Revolution: Merging of Colloid Science, Catalysis and Nanoelectronics

2008

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The incorporation of nanosciences into catalysis studies has become the most powerful approach to understanding reaction mechanisms of industrial catalysts and designing new-generation catalysts with high selectivity. Nanoparticle catalysts were synthesized via controlled colloid chemistry routes. Nanostructured catalysts such as nanodots and nanowires were fabricated with nanolithography techniques. Catalytic selectivity is dominated by several complex factors including the interface between active catalyst phase and oxide support, particle size and surface structure, and selective blocking of surface sites, etc. The advantage of incorporating nanosciences into the studies of catalytic selectivity is the capability of separating these complex factors and studying them one by one in different catalyst systems. The role of oxide-metal interfaces in catalytic reactions was investigated by detection of continuous hot electron flow in catalytic nanodiodes fabricated with shadow mask deposition technique. We found that the generation mechanism of hot electrons detected in Pt/TiO 2 nanodiode is closely correlated with the turnover rate under CO oxidation. The correlation suggests the possibility of promoting catalytic selectivity by precisely controlling hot electron flow at the oxide-metal interface. Catalytic activity of 1.7-7.2 nm monodispersed Pt nanoparticles exhibits particle size dependence, demonstrating the enhancement of catalytic selectivity via controlling the size of catalyst. Pt-Au alloys with different Au coverage grown on Pt(111) single crystal surface have different catalytic selectivity for four conversion channels of n-hexane, showing that selective blocking of catalytic sites is an approach to tuning catalytic selectivity. In addition, presence and absence of excess hydrogen lead to different catalytic selectivity for isomerization and dehydrocyclization of n-hexane on Pt(111) single crystal surface, suggesting that modification of reactive intermediates by the presence of coadsorbed hydrogen is one approach to shaping catalytic selectivity. Several challenges such as imaging the mobility of adsorbed molecules during catalytic reactions by high pressure STM and removing polymeric capping agents from metal nanoparticles remain.

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Section: Oxide-metal Interfacesupporting

confidence: 89%

The Nanoscience Revolution: Merging of Colloid Science, Catalysis and Nanoelectronics

2008

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“…These definitive experimental confirmations of the flow of hot, high kinetic energy electrons away from the platinum surface where the catalyzed exothermic reaction occurs to the metal-semiconductor interface brings into focus the early suggestions of Schwab [3,4], Szabo and Solymosi [5] as well as Langenbeck et al [6] who argued for the importance of the Schottky diode model of electron flow at oxide-metal interfaces for catalyzed reactions ranging from carbon monoxide oxidation, sulfur dioxide oxidation, formic acid decomposition, ethylene hydrogenation, cyclohexene hydrogenation/ dehydrogenation to ammonia synthesis [5,7]. Their experimental strategies were through the use of ''inverse catalyst'' systems that were fabricated by depositing oxides on films of transition metals that induced large changes in activation energies as a function of oxide thickness along with changes of turnover rates.…”

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confidence: 92%

The catalytic nanodiode. Its role in catalytic reaction mechanisms in a historical perspective

Somorjai

2005

Catal Lett

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Catalytic nanodiodes, Pt/TiO 2 or Pt/GaN produce continuous flow of hot electron current during carbon monoxide oxidation for hours in the 80-150°C temperature range at pressures of 100 Torr of O 2 and 40 Torr of CO. These observations provide proof of the Schottky diode model of oxide supported metal catalysis of many reactions that have been proposed by Schwab, Solymosi and others since the 1960s. The flow of hot electrons should influence chemistry at oxide-metal interfaces and the metal particle size dependence of catalytic activity and selectivity.KEY WORDS: catalytic nanodiode; electron flow in catalysis; hot electrons.We recently reported the continuous flow of hot electrons through a thin platinum film through semiconductor Schottky diodes of TiO 2 and GaN during the steady state catalytic oxidation of carbon monoxide (100 Torr of O 2 and 40 Torr of CO) in the 80-250°C range [1,2]. The scheme of the nanodiodes is shown in figure 1 along with the cross sections of the nanodiodes used successfully in these experiments. Platinum acts both as an electrode and as a catalyst, and its film thickness has to be of the order of the elastic mean free path of electrons or smaller so that the charges could arrive at the metal-semiconductor interface without attenuation. The measured barrier height at the metalsemiconductor interface of both Pt/TiO 2 and Pt/GaN nanodiodes is 1.2 eV, and thus the electrons must have kinetic energies greater than 1.2 eV to be collected by the electrode on the semiconductor side. High conversion efficiency was reported for Pt/TiO 2 (three electrons for every four CO 2 molecules formed) and lower efficiencies for the Pt/GaN diode that was explained by the greater thickness of the Pt film and its discontinuity.These definitive experimental confirmations of the flow of hot, high kinetic energy electrons away from the platinum surface where the catalyzed exothermic reaction occurs to the metal-semiconductor interface brings into focus the early suggestions of Schwab [3,4], Szabo and Solymosi [5] as well as Langenbeck et al.[6] who argued for the importance of the Schottky diode model of electron flow at oxide-metal interfaces for catalyzed reactions ranging from carbon monoxide oxidation, sulfur dioxide oxidation, formic acid decomposition, ethylene hydrogenation, cyclohexene hydrogenation/ dehydrogenation to ammonia synthesis [5,7]. Their experimental strategies were through the use of ''inverse catalyst'' systems that were fabricated by depositing oxides on films of transition metals that induced large changes in activation energies as a function of oxide thickness along with changes of turnover rates. However, these ideas of the importance of electron flow at the oxide-metal interfaces of these catalysts were strongly questioned [8] and found unacceptable by most catalyst researchers, mostly because of the absence of any experimental proof of current flow and its correlations to catalytic activity.In light of the high hot electron currents that were detected through the oxide-metal interfa...

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The precipitation of sparingly‐soluble alkaline‐earth metal and transition metal oxalates and mixed metal oxalates from aqueous solution: Ionic equilibria, crystalline phases and precipitation mechanisms

Packter¹

1981

Cryst Res and Technol

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The precipitations of alkaline-earth metal and transition metal oxalates, from aqueous solution and from excess alkali metal oxalate solution, are surveyed : also the coprecipitations of transition metal oxalates together with alkaline-earth metal oxalates. The ionic equilibria that influence these precipitations are examined, the crystalline precipitate phases are tabulated and precipitation mechanisms are analysed.Die Fallungen der Erdalkali-Metall-und tfbergangsmetall-Oxalate werden in einer ffbersicht dargestellt. Ebenso die Fallungen von Erdalkali-Metall-Oxalaten mit tfbergangsmetall-Oxalaten. Die Ionengleichgewichte werden bebrachtet, die kristallinen Phasen tabelliert und die Fallungsmechanismen analysiert.

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Über Mischsalzkontakte. XV. Selektive Hydrierung von Cyclopropan und Propen an Nickelkontakten. II

Cited by 12 publications

References 11 publications

The Nanoscience Revolution: Merging of Colloid Science, Catalysis and Nanoelectronics

The Nanoscience Revolution: Merging of Colloid Science, Catalysis and Nanoelectronics

The catalytic nanodiode. Its role in catalytic reaction mechanisms in a historical perspective

The precipitation of sparingly‐soluble alkaline‐earth metal and transition metal oxalates and mixed metal oxalates from aqueous solution: Ionic equilibria, crystalline phases and precipitation mechanisms

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