The decomposition of methanol on Au–Pt bimetallic clusters supported by a thin film of Al 2 O 3 /NiAl(100)

Liu

et al. 2021

J. Phys. Chem. Lett.

The size effect on the activity of a catalyst has been a focal issue since ideal catalysts were pursued, whereas that on the degradation of a catalyst, by reaction intermediates such as CO, is little discussed. We demonstrate that the dehydrogenation of methanol-d 4 on supported Rh nanoclusters precovered with CO (Rh −CO clusters) was obstructed, indicated by a decreased production of CO and D 2 ; the obstructive effect exhibits a remarkable dependence on the cluster size, with a minimum at a cluster diameter near 1.4 nm. The decreased production arose from a decreased reaction probability controlled by the increased activation energy for each dehydrogenation step (including formation of methoxy-d 3 ), adsorption energies of CO, and repulsion from the CO array on the Rh −CO surface. The effects of these factors in deactivating the clusters varied separately with the cluster size. Consequently, the size effect on the CO poisoning should be taken into account in engineering the cluster size to optimize the catalytic performance.

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confidence: 73%

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confidence: 98%

Dependence on Size of Supported Rh Nanoclusters in the Dehydrogenation of Methanol-d₄ Obstructed by CO

Liu

et al. 2021

J. Phys. Chem. Lett.

“…D2 desorption also reveals the type of element present at the cluster surface. In Pt-rich BCs, the tail of the D2 desorption feature extends even to 400 K, suggesting that D2 molecules are formed and desorbed from the Pt surface, 59 while no desorption higher than 350 K is observed in Ni-rich BCs. This is possibly due to the presence of a Ni enriched shell at the surface.…”

Section: Catalytic Activity Of Ptxni1-x Clustersmentioning

confidence: 99%

Composition-Tuned Pt-Skinned PtNi Bimetallic Clusters as Highly Efficient Methanol Dehydrogenation Catalysts

et al. 2019

Platinum is the most active anode and cathode catalyst in next-generation fuel cells using methanol as liquid source of hydrogen. Its catalytic activity can be significantly improved by alloying with 3d metals, although a precise tuning of its surface architecture is still required. Herein, we report the design of a highly active low temperature (below 0 • C) methanol dehydrogenation anode catalyst with reduced CO poisoning, based on ultra-low amount of precisely-defined PtxNi1-x (x = 0 to 1) bimetallic clusters (BCs) deposited on inert flat oxides by Cluster Beam Deposition (CBD). These BCs feature clear composition-dependent atomic arrangements and electronic structures stemming from their nucleation mechanism that are responsible for a volcano-type activity trend peaking at the Pt0.7Ni0.3 composition. Our calculations reveal that at this composition a cluster skin of Pt atoms with d-band centres downshifted by subsurface Ni atoms weakens the CO interaction that in turn triggers a significant increase in the methanol dehydrogenation activity.

“…Upon adsorption of CD 3 OD at 100 K, the spectra show several characteristic absorption lines; that at 984 cm –1 is assigned to the C–O stretching (ν(CO)) and that at 1125 cm –1 is assigned to the CD 3 symmetric deformation (δ s (CD 3 )) of CD 3 OD* (top spectrum in Figure a); a broad absorption line centered at 2440 cm –1 is assigned to O-D stretching (ν(OD)), a doublet at 2243 and 2214 cm –1 is assigned to the combination ν as (CD 3 ) + 2δ s (CD 3 ), and a narrow line at 2071 cm –1 is assigned to symmetric CD 3 stretch (ν s (CD 3 )) of CD 3 OD* (top spectrum in Figure b). − These features resemble closely those of CD 3 OD* on supported Pt clusters, Au–Pt, and Au–Rh bimetallic clusters. ,, When the temperature was increased to 135 K, all absorption lines attenuated significantly because multilayer CD 3 OD* desorbed from the surface; a slight red shift of δ s (CD 3 ) and ν(CO) lines resulted because the signals were contributed primarily by monolayer CD 3 OD* (third spectrum in Figure a). At 155 K, the signals of ν(OD) and ν as (CD 3 ) + 2δ s (CD 3 ) almost vanished because CD 3 OD* decreased and the O–D stretching motion of monolayer CD 3 OD* was nearly parallel to the surface. ,, On annealing further to 175–225 K, the spectra altered significantly; the δ s (CD 3 ) and ν s (CD 3 ) lines shifted negatively to 1103 and 2056 cm –1 , respectively, indicating the formation of CD 3 O* and hence the cleavage of the O–D bond of CD 3 OD*; ,, a new absorption feature appeared at about 1023 cm –1 , ascribed to the ωCD 2 mode of CD 2 O* . The negative shifts of δ s (CD 3 ) and ν s (CD 3 ) lines were observed for investigated V coverages ≥0.5 ML whereas the new absorption was observed only for 4.0 ML V. As the orientations of CD 3 O* and CD 2 O* were unknown, a precise estimation or comparison of their quantities was difficult.…”

Section: Resultsmentioning

confidence: 99%

Catalyzed Decomposition of Methanol-d₄ on Vanadium Nanoclusters Supported on an Ultrathin Film of Al₂O₃/NiAl(100)

Ansari

Dutta

et al. 2022

J. Phys. Chem. C

Self Cite

The decomposition of methanol-d 4 on vanadium (V) nanoclusters grown by vapor deposition of V on an ordered thin film of Al2O3/NiAl(100) was studied under ultrahigh-vacuum conditions and with various surface probe techniques and calculations based on density functional theory. The V clusters had mean diameter 1.55–2.10 nm and height 0.46–0.66 nm evolving with their coverage; they grew in a bcc phase and primarily in orientation (001); the lattice contracted 4% (relative to the bulk) to match structurally better the alumina surface. The methanol-d 4 adsorbed on the V clusters decomposed largely through the formation of methoxy-d 3 (denoted as CD3O*) at 175–225 K and subsequent cleavage of the C–O bond, yielding methyl-d 3 (CD3*), at temperature ≥350 K; CD3* either combined with surface deuterium (D*) and desorbed as methane-d 4 (CD4(g)) or dehydrogenated to supply more D* to assist the formation of molecular deuterium (D2(g)). As a measure of the reactivity, the quantities of CD4(g) and D2(g) produced per surface V site exhibited an evident dependence on the cluster size. Both these productions were inhibited on small clusters but increased with the cluster size; the production of D2(g) per surface site was saturated about that from V thin films, whereas that of CD4(g) attained a maximum at a cluster diameter near 2.0 nm but decreased, with further increasing size, to a value near that from V thin films. We argue that the inactivity of small V clusters arose from an increased energy barrier for scission of the C–O bond of CD3O*, which is a critical step of methanol-d 4 decomposition, on two-dimensional structures of small clusters; the separate trends of production of CD4(g) and D2(g) on larger clusters are attributable to the competition of CD3* and D* for D*.