Preparation and characterization of very highly dispersed iridium on Al2O3 and SiO2

Kip, BJ; Grondelle, van J Joop; Martens, Jha; Prins, R.

doi:10.1016/s0166-9834(00)82564-6

Cited by 35 publications

(13 citation statements)

References 36 publications

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“…In our laboratory, Pt, Rh, and Ir catalysts supported on A1203, SiOZ, and TiOz have been studied in the hydrogenation of carbon monoxide to hydrocarbons and oxygenated products. We have also used hydrogen chemisorption to characterize the highly dispersed supported metal catalysts and have obtained HIM values exceeding unity for Rh and Pt catalysts (34-36) and HIM values even exceeding 2.0 for supported Ir systems (37). Because of a lack of information on the hydrogen-to-metal stoichiometry for very small metal particles, we were unable to calculate the dispersion from the chemisorption results.…”

Section: Introductionmentioning

confidence: 99%

“…EXPERIMENTAL Preparation of the catalysts. Pt, Ir, and Rh catalysts were prepared from RhC& and IrC13 via the incipient wetness technique (34, 35,37), from Pt(NH&(OH)z and Rh(NO& via the ion-exchange technique (36,44), and from h-Cl3 via the urea method (37). In the last method, the pH of a suspension of the support and metal ions in water is increased slowly by means of the decomposition of urea (4.5).…”

Section: Introductionmentioning

confidence: 99%

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Determination of metal particle size of highly dispersed Rh, Ir, and Pt catalysts by hydrogen chemisorption and EXAFS

Kip

Duivenvoorden

Koningsberger

et al. 1987

Journal of Catalysis

305

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Determination of metal particle size of highly dispersed Rh, Ir, and Pt catalysts by hydrogen chemisorption and EXAFS

Kip

Duivenvoorden

Koningsberger

et al. 1987

Journal of Catalysis

305

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“…Reports in the literature indicate that smaller Ir particles require a higher reduction temperature compared to those for larger particles [41,42]. Nevertheless, the reduction of Ir-based catalysts is a relatively complex phenomenon that largely depends on the processing conditions and thermal history of each sample (Ir reduction is an autocatalytic process and IrO x are volatile species detrimental to metal dispersion) [43]. The Ni catalyst TPR profile also is consistent with literature results for catalysts with a similar particle size (6 nm) [44,45].…”

Section: Metal Particle Size Tem (Nm)mentioning

confidence: 99%

Methane and Ethane Steam Reforming over MgAl2O4-Supported Rh and Ir Catalysts: Catalytic Implications for Natural Gas Reforming Application

et al. 2019

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Solar concentrators employed in conjunction with highly efficient micro- and meso-channel reactors offer the potential for cost-effective upgrading of the energy content of natural gas, providing a near-term path towards a future solar-fuel economy with reduced carbon dioxide emissions. To fully exploit the heat and mass transfer advantages offered by micro- and meso-channel reactors, highly active and stable natural gas steam reforming catalysts are required. In this paper, we report the catalytic performance of MgAl2O4-supported Rh (5 wt.%), Ir (5 wt.%), and Ni (15 wt.%) catalysts used for steam reforming of natural gas. Both Rh- and Ir-based catalysts are known to be more active and durable than conventional Ni-based formulations, and recently Ir has been reported to be more active than Rh for methane steam reforming on a turnover basis. Thus, the effectiveness of all three metals to perform natural gas steam reforming was evaluated in this study. Here, the Rh- and Ir-supported catalysts both exhibited higher activity than Ni for steam methane reforming. However, using simulated natural gas feedstock (94.5% methane, 4.0% ethane, 1.0% propane, and 0.5% butane), the Ir catalyst was the least active (on a turnover basis) for steam reforming of higher hydrocarbons (C2+) contained in the feedstock when operated at <750 °C. To further investigate the role of higher hydrocarbons, we used an ethane feed and found that hydrogenolysis precedes the steam reforming reaction and that C–C bond scission over Ir is kinetically slow compared to Rh. Catalyst durability studies revealed the Rh catalyst to be stable under steam methane reforming conditions, as evidenced by two 100-hour duration experiments performed at 850 and 900 °C (steam to carbon [S/C] molar feed ratio = 2.0 mol). However, with the natural gas simulant feed, the Rh catalyst exhibited catalyst deactivation, which we attribute to coking deposits derived from higher hydrocarbons contained in the feedstock. Increasing the S/C molar feed ratio from 1.5 to 2.0 reduced the deactivation rate and stable catalytic performance was demonstrated for 120 h when operated at 850 °C. However, catalytic deactivation was observed when operating at 900 °C. While improvements in steam reforming performance can be achieved through choice of catalyst composition, this study also highlights the importance of considering the effect of higher hydrocarbons contained in natural gas, operating conditions (e.g., temperature, S/C feed ratio), and their effect on catalyst stability. The results of this study conclude that a Rh-supported catalyst was developed that enables very high activities and excellent catalytic stability for both the steam reforming of methane and other higher hydrocarbons contained in natural gas, and under conditions of operation that are amendable to solar thermochemical operations.

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“…The catalysts were prepared from RhCl 3 and IrCl 3 via the incipient wetness technique (5,6,8), from Pt<NH 3 )4(QH)2 and RheN0 3 )3 via the ionexchange technique (7,9), and from IrCl 3 ',ia the urea method (8). Y-Al 2 0 3 and SiO 2 were used as supports.…”

Section: It Experimentalmentioning

confidence: 99%

“…However, HlMtotal values exceeding unity have been obtained for supported Pt, Rh, and Ir systems (2)(3)(4)(5)(6)(7)(8), In these cases the dispersions cannot be calculated straightforwardly, because of the uncertainty in the adsorption stoichiometry. Therefore we used the EXAFS <Extended X-ray Absorption Fine Structure) technique to determine the average metal-metal coordination number in the metal particles, which is related to the particle size.…”

Section: Introductionmentioning

confidence: 99%

DETERMINATION OF THE METAL PARTICLE SIZE OF SUPPORTED Pt, Rh, AND Ir CATALYSTS. A CALIBRATION OF HYDROGEN CHEMISORPTION BY EXAFS

et al. 1986

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Hydrogen chemisorption measurements of highly dispersed Pt, Rh, and Ir catalysts yielded H/M values exceeding unity. These results cannot be used straightforwardly to determine the average metal particle size, because the H/M stoichiometry on the surface is unknown. EXAFS measurements were performed to determine the metal particle size and thereby, to calibrate the hydrogen chemisorption results. The high hydrogen chemisorption values can be explained best by assuming H/M surface stoichiometries exceeding unity. The adsorption stoichiometry differs among Pt, Rh, and Ir in the order H/Pt < H/Rh < H/Ir, analogous to the order in stability of the corresponding metal polyhydride complexes

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Preparation and characterization of very highly dispersed iridium on Al2O3 and SiO2

Cited by 35 publications

References 36 publications

Determination of metal particle size of highly dispersed Rh, Ir, and Pt catalysts by hydrogen chemisorption and EXAFS

Determination of metal particle size of highly dispersed Rh, Ir, and Pt catalysts by hydrogen chemisorption and EXAFS

Methane and Ethane Steam Reforming over MgAl2O4-Supported Rh and Ir Catalysts: Catalytic Implications for Natural Gas Reforming Application

DETERMINATION OF THE METAL PARTICLE SIZE OF SUPPORTED Pt, Rh, AND Ir CATALYSTS. A CALIBRATION OF HYDROGEN CHEMISORPTION BY EXAFS

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