“…The adsorption of CO on hydrated 5 wt % Ru/Al 2 O 3 results in ν CO absorbance features at 2049, 1992, and 1924 cm -1 (Figure ). While the ν CO absorbance at 2049 cm -1 may be attributed to CO adsorption on the Al 2 O 3 support, this band is tentatively assigned as a Ru species since CO should preferentially adsorb to Ru rather than the support ,,− and the 2049 cm -1 absorbance feature is much more intense on the reduced Ru/Al 2 O 3 than it was on Al 2 O 3 . 8 ATR-FTIR spectra of CO adsorption on 5 wt % Ru/Al 2 O 3 collected as a function of time.…”
Section: Resultsmentioning
confidence: 94%
“…There have been several models proposed to explain the appearance of three ν CO absorbance features when CO adsorbs on supported Ru catalysts . In all of these models, the ν CO absorbance feature at 2020−2040 cm -1 is attributed to a Ru x -CO species. ,,− The ν CO absorbance features at 2140 and 2075 cm -1 have been assigned as the symmetric and asymmetric stretches of two CO molecules in gem-dicarbonyl, Ru I (CO) 2 , or as CO adsorption on low coordination edge and corner metal atoms with more than one adsorbed CO, and as the vibration of CO adsorbed on a surface oxide and on a Ru atom perturbed by a nearby O atom, respectively . Since the relative intensities of the ν CO absorbances at 2049, 1992, and 1924 cm -1 (Figures −10) depend upon the amount of coadsorbed water on the surface and the TPD curve is consistent with three CO bonding sites, these results indicate that there are three different adsorption sites on hydrated Ru/Al 2 O 3 .…”
The adsorption of CO on hydrated 5 wt % Ru/Al 2 O 3 produced ν CO absorbance features at ∼2048, 1992, and 1924 cm -1 that are red-shifted by 50-116 cm -1 from those seen in the absence of water (2020-2040, 2080, and 2140 cm -1 ). This red-shift most likely arises from dipole-dipole interaction between coadsorbed CO and water molecules since (1) the exact frequency of the ν CO absorbance feature depends upon the amount of coadsorbed water and (2) the presence of flowing liquid water further red-shifts the frequencies. These ν CO absorbance features are uncorrelated, since the relative intensities of the ν CO absorbances at 2049, 1992, and 1924 cm -1 depend on the amount of coadsorbed water and CO on the surface. Temperature programmed desorption done with TGA-MS indicated three different high-temperature CO 2 desorption peaks. These CO 2 peaks (T ≈ 350, 400, and 550 °C) are most likely the result of the oxidation of adsorbed CO reacting with surface adsorbed water (CO ads + H 2 O ads f H 2 + CO 2 ) and/or the disproportionation of CO (2CO f C ads + CO 2 ). These high-temperature CO 2 desorption peaks suggest that CO strongly adsorbs to hydrated 5 wt % Ru/Al 2 O 3 catalysts. This is corroborated by the fact that intensities of the ν CO absorbance features do not decrease in the presence of flowing liquid water.
“…The adsorption of CO on hydrated 5 wt % Ru/Al 2 O 3 results in ν CO absorbance features at 2049, 1992, and 1924 cm -1 (Figure ). While the ν CO absorbance at 2049 cm -1 may be attributed to CO adsorption on the Al 2 O 3 support, this band is tentatively assigned as a Ru species since CO should preferentially adsorb to Ru rather than the support ,,− and the 2049 cm -1 absorbance feature is much more intense on the reduced Ru/Al 2 O 3 than it was on Al 2 O 3 . 8 ATR-FTIR spectra of CO adsorption on 5 wt % Ru/Al 2 O 3 collected as a function of time.…”
Section: Resultsmentioning
confidence: 94%
“…There have been several models proposed to explain the appearance of three ν CO absorbance features when CO adsorbs on supported Ru catalysts . In all of these models, the ν CO absorbance feature at 2020−2040 cm -1 is attributed to a Ru x -CO species. ,,− The ν CO absorbance features at 2140 and 2075 cm -1 have been assigned as the symmetric and asymmetric stretches of two CO molecules in gem-dicarbonyl, Ru I (CO) 2 , or as CO adsorption on low coordination edge and corner metal atoms with more than one adsorbed CO, and as the vibration of CO adsorbed on a surface oxide and on a Ru atom perturbed by a nearby O atom, respectively . Since the relative intensities of the ν CO absorbances at 2049, 1992, and 1924 cm -1 (Figures −10) depend upon the amount of coadsorbed water on the surface and the TPD curve is consistent with three CO bonding sites, these results indicate that there are three different adsorption sites on hydrated Ru/Al 2 O 3 .…”
The adsorption of CO on hydrated 5 wt % Ru/Al 2 O 3 produced ν CO absorbance features at ∼2048, 1992, and 1924 cm -1 that are red-shifted by 50-116 cm -1 from those seen in the absence of water (2020-2040, 2080, and 2140 cm -1 ). This red-shift most likely arises from dipole-dipole interaction between coadsorbed CO and water molecules since (1) the exact frequency of the ν CO absorbance feature depends upon the amount of coadsorbed water and (2) the presence of flowing liquid water further red-shifts the frequencies. These ν CO absorbance features are uncorrelated, since the relative intensities of the ν CO absorbances at 2049, 1992, and 1924 cm -1 depend on the amount of coadsorbed water and CO on the surface. Temperature programmed desorption done with TGA-MS indicated three different high-temperature CO 2 desorption peaks. These CO 2 peaks (T ≈ 350, 400, and 550 °C) are most likely the result of the oxidation of adsorbed CO reacting with surface adsorbed water (CO ads + H 2 O ads f H 2 + CO 2 ) and/or the disproportionation of CO (2CO f C ads + CO 2 ). These high-temperature CO 2 desorption peaks suggest that CO strongly adsorbs to hydrated 5 wt % Ru/Al 2 O 3 catalysts. This is corroborated by the fact that intensities of the ν CO absorbance features do not decrease in the presence of flowing liquid water.
“…The mean particle size is subnanometric for Ru(Cl)/Al/M and 1.5 nm for Ru(acac)/Al/M. [44,45], which could explain the lower Ru o /Ru (total) ratios. However, the effect of electron-withdrawing species cannot be invoked to explain the lower Ru 0 /Ru (total) ratios of Ru(acac)/Al/M.…”
Section: Textural and Morphological Characterizationmentioning
Ru catalysts supported on alumina coated monoliths has been prepared employing three different precursor, which are ruthenium chloride, ruthenium nitrosyl nitrate and ruthenium acetyl acetonate, by an equilibrium adsorption method. The Ru particle sizes could be controlled varying the metal precursor salt. Among the prepared catalysts, Ru catalyst prepared from nytrosyl nitrate exhibited the highest activity which is concomitant to the largest mean Ru particle size of 3.5 nm. The values of the apparent activation energy calculated from the Arrhenius equation are according to the Temkin-Phyzev model, indicating that the recombinative desorption of N ad-atoms is the ratedetermining step of the reaction. However, the ratio between the kinetic orders with respect to ammonia and hydrogen (-α/β), is not in agreement to the valued predict by Temkin formalism. This fact could be related to the different operational conditions used during the reaction, and/or catalyst nature, but not to any change on the controlling step of the reaction.
“…The main drawback of those metal nanoparticles is lack of stability, − partly because of agglomerates formation of the metal nanoparticles capped with organic molecules during the photocatalytic H 2 production. Such an agglomeration problem of metal nanoparticles may be improved by the application of size-controlled nanoparticles to catalysts on a solid support, because controlled and precise growth of nanoparticles with the desired shape and size can be tuned by altering the morphology of the support as reported in the field of heterogeneous catalysis. − However, there have been no systematic studies on the effects of supports on photocatalytic H 2 production with metal nanoparticles used as H 2 -evolution catalysts.…”
Effects of various metal oxide supports
(SiO2, SiO2–Al2O3, TiO2, CeO2, and MgO) on the catalytic reactivity
of ruthenium nanoparticles
(RuNPs) used as a hydrogen-evolution catalyst have been evaluated
in photocatalytic hydrogen evolution using 2-phenyl-4-(1-naphthyl)quinolinium
ion (QuPh+–NA) and dihydronicotinamide adenine dinucleotide
(NADH) as a photocatalyst and an electron donor, respectively. The
3 wt % Ru/SiO2 catalyst freshly prepared by an impregnation
method exhibited the highest catalytic reactivity among RuNPs supported
on various metal oxides, which was nearly the same as that of commercially
available Pt nanoparticles (PtNPs) with the same metal weight. However,
the initial catalytic reactivity of 3 wt % Ru/SiO2 was
lost after repetitive use, whereas the catalytic reactivity of PtNPs
was maintained under the same experimental conditions. The recyclability
of the 3 wt % Ru/SiO2 was significantly improved by employing
the CVD method for preparation. The initial catalytic reactivity of
0.97 wt % Ru/SiO2 prepared by the CVD method was higher
than that of 2 wt % Ru/SiO2 prepared by the impregnation
method despite the smaller Ru content. The total amount of evolved
hydrogen normalized by the weight of Ru in 0.97 wt % Ru/SiO2 was 1.7 mol gRu
–1, which is now close
to that normalized by the weight of Pt in PtNPs (2.0 mol gPt
–1). Not only the preparation method but also the
morphology of SiO2 supports affected significantly the
catalytic activity of Ru/SiO2. The Ru/SiO2 catalyst
using nanosized SiO2 with undefined shape exhibited higher
catalytic activity than Ru/SiO2 catalysts using mesoporous
SiO2 or spherical SiO2. The kinetic study and
TEM observation of the Ru/SiO2 catalysts suggest that the
microenvironment of RuNPs on SiO2 surfaces plays an important
role to exhibit the high catalytic performance in the photocatalytic
hydrogen production.
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