Hydrogen Effects in Metal Catalysts

Paál, Z.; Menon, P.G.

doi:10.1080/01614948308079667

Cited by 149 publications

(62 citation statements)

References 141 publications

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“…The peak intensities of β-PdH x decomposition were increasing with the Pd content, which is ascribed to the Pd crystallite siz [26]. A broad positive peak with onset temperature of 475˚C centred at 700˚C was observed, which corresponds to the hydrogen consumption together elution of carbonaceous deposits [27]. However, this hydrogen consumption was attributed to the spill-over phenomenon in CMS supported catalysts.…”

Section: Temperature Programmed Reduction Studiesmentioning

confidence: 88%

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Effect of Alkali Carbonate/Bicarbonate on Citral Hydrogenation over Pd/Carbon Molecular Sieves Catalysts in Aqueous Media

Krishna

Ramakrishna

Soni

et al. 2016

MRC

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The efficient citral hydrogenation was achieved in aqueous media using Pd/CMS and alkali additives like K 2 CO 3 . The alkali concentrations, reaction temperature and the Pd metal content were optimized to enhance the citral hydrogenation under aqueous media. In the absence of alkali, citral hydrogenation was low and addition of alkali promoted to ~92% hydrogenation without reduction in the selectivity to citronellal. The alkali addition appears to be altered the palladium sites. The pore size distribution reveals that the pore size of these catalysts is in the range of 0.96 to 0.7 nm. The palladium active sites are also quite uniform based on the TPR data. The catalytic parameters are correlated well with the activity data.

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Section: Temperature Programmed Reduction Studiesmentioning

confidence: 88%

“…This peak corresponds to elution of hydrogen by decomposition of β-PdH x [26] [27]. The peak intensities of β-PdH x decomposition were increasing with the Pd content, which is ascribed to the Pd crystallite siz [26].…”

Section: Temperature Programmed Reduction Studiesmentioning

confidence: 97%

Effect of Alkali Carbonate/Bicarbonate on Citral Hydrogenation over Pd/Carbon Molecular Sieves Catalysts in Aqueous Media

Krishna

Ramakrishna

Soni

et al. 2016

MRC

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“…1 Generally, two types of hydrogen are observed, weakly and strongly bonded to the metal. [2][3][4][5][6][7][8][9][10] Weakly (or reversibly) adsorbed hydrogen is defined as hydrogen, which can easily be desorbed, for example, by evacuating for 10 min at low temperatures. 11 Strongly (or irreversibly) adsorbed hydrogen is defined as hydrogen that remains on the metal surface after evacuation at room temperature.…”

Section: Introductionmentioning

confidence: 99%

The Nature of the Pt−H Bonding for Strongly and Weakly Bonded Hydrogen on Platinum. A XAFS Spectroscopy Study of the Pt−H Antibonding Shaperesonance and Pt−H EXAFS

2001

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A long-standing problem in the research of H 2 chemisorption on supported Pt catalysts is the unclarity about the difference in nature of the Pt-H bonding for weakly and strongly bonded hydrogen. On the basis of Pt-Pt EXAFS and a newly developed XANES analysis of the Pt L 2 and L 3 edges, it will be shown that both types of hydrogen are truly chemisorbed species. The EXAFS analysis shows a similar contraction of the Pt-Pt bond irrespective of the removal of weakly or strongly bound hydrogen, indicating a similar nature for both interactions. Moreover, the analysis of the L 2 and L 3 X-ray absorption edges shows unambiguously the presence of a Pt-H antibonding state for both the weakly and strongly bonded hydrogen. This is a clear indication for chemisorption of hydrogen for both types of hydrogen. The Pt-H EXAFS shows a smaller Pt-H bond length in the case of strongly adsorbed, which is in correlation with the expected strength of the Pt-H bond.

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“…56 No supersaturation-segregation process is necessary. Chemisorbed species such as H can significantly alter a catalyst surface 39 and thus aid diffusive transport and SWNT nucleation dependent on temperature and pressure.…”

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confidence: 99%

“…39 Hydrogen penetration into subsurface layers can loosen the catalyst surface 39 and may give higher carbon diffusivities for low-temperature SWNT nucleation. 19 Figure 2e shows a HRTEM image of a 0.1 nm Fe film on an e-beam transparent silicon nitride membrane after SWNT CVD at 500°C.…”

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confidence: 99%

Catalytic Chemical Vapor Deposition of Single-Wall Carbon Nanotubes at Low Temperatures

et al. 2006

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We report surface-bound growth of single-wall carbon nanotubes (SWNTs) at temperatures as low as 350°C by catalytic chemical vapor deposition from undiluted C 2 H 2 . NH 3 or H 2 exposure critically facilitates the nanostructuring and activation of sub-nanometer Fe and Al/Fe/Al multilayer catalyst films prior to growth, enabling the SWNT nucleation at lower temperatures. We suggest that carbon nanotube growth is governed by the catalyst surface without the necessity of catalyst liquefaction.Carbon nanotubes (CNTs) have been a driving force for current advances in nanotechnology, both on an applied and on a fundamental level. Single-wall carbon nanotubes have shown the highest Young's modulus and highest axial thermal conductivity of any solid. Moreover, SWNTs have the highest current carrying capacity of any conductor, which makes them an attractive electronic, sensing, or heat sinking material for nano-electromechanical systems (NEMS) and future (hybrid) integrated circuitry. 1,2Defect-free SWNT synthesis is generally thought to require high temperatures (T). 3 This belief arises from the success of high-T deposition processes. Arc-discharge, laser ablation, and high-pressure CO conversion with inherent (local) temperatures in the order of 1000-4000°C have been optimized mainly for bulk CNT production. 3 For device fabrication, these techniques heavily rely on purification from other carbon allotropes and an indirect postgrowth assembly via stable suspensions. In comparison, catalytic chemical vapor deposition (CVD) allows selective, aligned CNT growth directly onto a substrate and thus presently is the only economically viable process for integrating CNTs into a device. 1,[4][5][6] This approach, however, exposes the substrate to the CNT growth temperature and atmosphere, which creates a need for less aggressive, low T processing conditions. Present back-end CMOS technology allows a maximum temperature of 400-450°C, the limit being set by the mechanical integrity of low dielectric constant intermetal dielectrics. 7 Thermal CVD of SWNTs has been reported at 550°C in furnace 8 and cold wall systems. 9 In situ environmental transmission electron microscopy (TEM) experiments show SWNT nucleation at 480°C. 10 Random-network FETs have been fabricated with SWNTs grown at 450°C by remote plasma-enhanced (PE) CVD.11 However, the high temperatures of bulk production techniques still dominate growth model considerations with the assumption that the catalyst cluster has to be liquefied and that the catalyst bulk is ratecontrolling.12,13 These considerations are also transferred to surface-bound CVD. 14 CNT growth below 500°C is not thought to be possible based on calculations of size-corrected melting points 14 and carbon saturation. 15In this Letter, we report SWNT growth at temperatures below 450°C by thermal CVD at cold wall conditions and demonstrate field effects in as-integrated SWNT FETs. We use evaporated thin catalyst films, which allow accurate patterning by standard lithography techniques and thus compa...

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Hydrogen Effects in Metal Catalysts

Cited by 149 publications

References 141 publications

Effect of Alkali Carbonate/Bicarbonate on Citral Hydrogenation over Pd/Carbon Molecular Sieves Catalysts in Aqueous Media

Effect of Alkali Carbonate/Bicarbonate on Citral Hydrogenation over Pd/Carbon Molecular Sieves Catalysts in Aqueous Media

The Nature of the Pt−H Bonding for Strongly and Weakly Bonded Hydrogen on Platinum. A XAFS Spectroscopy Study of the Pt−H Antibonding Shaperesonance and Pt−H EXAFS

Catalytic Chemical Vapor Deposition of Single-Wall Carbon Nanotubes at Low Temperatures

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