Individual Heat of Adsorption of Adsorbed CO Species on Palladium and Pd–Sn Nanoparticles Supported on Al₂O₃ by Using Temperature-Programmed Adsorption Equilibrium Methods

Abstract

The present article is dedicated to the adsorption of CO on reduced 2% Pd/Al 2 O 3 and 2% Pd-x% Sn/Al 2 O 3 (weight %, x = 2 or 5 wt %) in the 300−713 K temperature range to study the geometric and electronic effects of Sn on the palladium adsorption sites. Using Fourier transform infrared (FTIR) spectroscopy, it is shown that the insertion of Sn leads to (a) the total disappearance of the Pd sites forming bridged CO species (denoted as "B"), which are the dominant species on Pd 0 particles and (b) a significant increase in the Pd sites forming linear CO species (denoted as "L"). This is ascribed to a geometric effect of Sn that dilutes the superficial palladium sites. The measurement of the individual heats of adsorption of the different adsorbed CO species by using two original temperature-programmed adsorption equilibrium methods (denoted AEIR and TPAE) allows the estimation of the electronic effect of Sn on the Pd sites. On 2% Pd/ Al 2 O 3 , in parallel to the formation of two strongly adsorbed B CO species, two linear L1 Pd 0 and L2 Pd 0 CO species are formed, which exhibit different heats of adsorption. For the dominant L1 Pd 0 CO species, the heat of adsorption decreases linearly, from 92 kJ/mol to 54 kJ/mol, as its coverage increases at coverage 0 and 1, respectively, while that of the L2 Pd 0 species is >165 kJ/mol at coverage 1. On the two Pd−Sn containing particles, two linear CO species are formed denoted L1 2Pd−xSn and L2 2Pd−xSn with x = 2 or 5. The L1 2Pd−xSn species dominates the CO adsorption on the two solids. It is shown that its heat of adsorption (which is slightly dependent on x) linearly varies with its coverage: ∼90 kJ/mol and ∼50 kJ/mol at low and high coverage, respectively. The comparison with the heat of adsorption of L1 Pd 0 indicates that the electronic effect of tin is very modest, compared to its geometric effect. This conclusion is consistent with literature data dedicated to DFT calculation. Moreover, (a) XRD and TEM/ EDX analysis suggest that bimetallic particles such as Pd 3 Sn and Pd 2 Sn are present and (b) the impact of tin on the H 2 chemisorption on Pd 0 sites are presented.

A Contribution to the Experimental Microkinetic Approach of Gas/Solid Heterogeneous Catalysis: Measurement of the Individual Heats of Adsorption of Coadsorbed Species by Using the AEIR Method

“…Similarly the AEIR method allows studying the geometric and electronic effects due to the formation of bimetallic particles via the changes in the nature of the adsorbed CO species and in their heats of adsorption respectively. For instance, the AEIR method reveals that the insertion of Sn in Pd particles [91] leads to the total disappearance of the bridged CO species due to a geometric effect. Moreover, the heat of…”

“…Similarly the AEIR method allows studying the geometric and electronic effects due to the formation of bimetallic particles via the changes in the nature of the adsorbed CO species and in their heats of adsorption respectively. For instance, the AEIR method reveals that the insertion of Sn in Pd particles [91] leads to the total disappearance of the bridged CO species due to a geometric effect. Moreover, the heat of adsorption of the L CO species on Pd • sites, which varies linearly with its coverage from E 0 = 92 kJ/mol to E 1 = 54 kJ/mol on monometallic particles, is slightly modified on the Pd-Sn bimetallic particles: E 0 = 90 kJ/mol and E 1 = 50 k/mol, indicating a very small electronic effect.…”

“…Similarly, Meunier et al have used the AEIR method in DRIFT mode to study the impacts of the insertion of Zn on Pd • sites of a Pd/CeO 2 catalyst [92]. The insertion on Zn suppresses the B CO species due to a geometric effect (as for the Pd-Sn particles [91]) whereas the heat of adsorption of the L CO species for Pd-Zn particles reduced at 773 K varies from E 0 = 105 ± 5 kJ/mol to E 1 = 68 ± 5 kJ/mol revealing a modest electronic effect of Zn. The same group has used the AEIR method to study the electronic effect of the insertion on Sn in Pt • particles supported on Al 2 O 3 revealing a strong electronic effect with a heat of adsorption at low coverage half of that on the monometallic particles [93].…”

Sinter-Resistant Nanoparticle Catalysts Achieved by 2D Boron Nitride-Based Strong Metal–Support Interactions: A New Twist on an Old Story

“… 28 As shown in Figure 2 G, CO adsorption by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements at room temperature for both Pd/h-BN-SMSI and Pd/h-BN samples were performed. For the Pd/h-BN-SMSI material, the bands at 2117 and 2171 cm –1 were attributed to gaseous CO, and the band at 2046 cm –1 was assigned to linearly adsorbed CO. 56 Comparatively, in the DRIFTS result of Pd/h-BN, besides linearly adsorbed CO, additional bands at 1914 and 1955 cm –1 appeared, ascribed to two types of bridged adsorption of CO species on the bare Pd NPs, 56 which completely disappeared for Pd/h-BN-SMSI. The presence of linear CO adsorption for Pd/h-BN-SMSI resulted from the nanoporous architecture of h-BN layer, 49 supplying channels for CO molecules to go through and interact with the inner Pd NPs.…”

Fabrication of Crumpled Ball-Like Nickel Doped Palladium-Iron Oxide Hybrid Nanoparticles with Controlled Morphology as Effective Catalyst for Suzuki–Miyaura Coupling Reaction

“…In recent years, the fabrication of metal hybrid nanoparticles has been widely accepted as one method to increase the catalytic activity, selectivity, and stability of metal nanoparticles [1][2][3]. The catalytic performances of metal hybrid nanoparticles can be tuned by controlling the elemental distribution in the surface, intermetallic charge transfer, and lattice strain [4].…”