Adsorption and Reaction of CO on (Pd–)Al2O3 and (Pd–)ZrO2: Vibrational Spectroscopy of Carbonate Formation

Abstract

γ-Alumina is widely used as an oxide support in catalysis, and palladium nanoparticles supported by alumina represent one of the most frequently used dispersed metals. The surface sites of the catalysts are often probed via FTIR spectroscopy upon CO adsorption, which may result in the formation of surface carbonate species. We have examined this process in detail utilizing FTIR to monitor carbonate formation on γ-alumina and zirconia upon exposure to isotopically labelled and unlabelled CO and CO2. The same was carried out for well-defined Pd nanoparticles supported on Al2O3 or ZrO2. A water gas shift reaction of CO with surface hydroxyls was detected, which requires surface defect sites and adjacent OH groups. Furthermore, we have studied the effect of Cl synthesis residues, leading to strongly reduced carbonate formation and changes in the OH region (isolated OH groups were partly replaced or were even absent). To corroborate this finding, samples were deliberately poisoned with Cl to an extent comparable to that of synthesis residues, as confirmed by Auger electron spectroscopy. For catalysts prepared from Cl-containing precursors a new CO band at 2164 cm−1 was observed in the carbonyl region, which was ascribed to Pd interacting with Cl. Finally, the FTIR measurements were complemented by quantification of the amount of carbonates formed via chemisorption, which provides a tool to determine the concentration of reactive defect sites on the alumina surface.

Operando Surface Spectroscopy and Microscopy during Catalytic Reactions: From Clusters via Nanoparticles to Meso‐Scale Aggregates

“…Adsorbed CO on Au 0 (2130 cm −1 ) was observed up to 120 °C (note that any Au surface atom on a cluster is low‐coordinated). [ 231 ] Monodentate carbonates (1468 cm −1 ) [ 71,162,243 ] developed in the lower wavenumber region (Figure 8d), likely located on ceria or close to the metal/oxide interface. Increasing IR bands characterizing surface SO 3 (or S 2 O 7 −2 ) and SO 4 (SO, SOCe) were also detected, [ 244 ] whereas bulk SO 4 was absent (missing bands at 1196, 1128 cm −1 ).…”

“…Vibrational infrared (IR) spectroscopy of adsorbed species and the catalyst material itself is a versatile operando method, [67,68,[73][74][75]85,[161][162][163][164][165][166] based on the absorption of broadband IR radiation (I 0 ) as measured by Fourier-transform (FT) spectrometers. As IR is not surface-specific, keeping the IR beam path in the gas phase short limits IR gas phase absorption (gas phase bands hold information on reactants and products, but may obscure surface species).…”

“…[159,186,[279][280][281][282] In addition, CO adsorption is frequently used to characterize the accessible surface sites. [36,73,159,162,282,283] It is well-accepted that particle size and shape and the metal/support interface govern the catalytic performance in many cases. Sites at metal/ oxide interface (colored light blue in Figure 1c), termed perimeter (adlineation) sites or (triple) phase boundary sites, are often even considered to be most active.…”

Support Effects on the Activity of Ni Catalysts for the Propane Steam Reforming Reaction

“…This can be clearly seen in the spectrum obtained at 500 °C (trace i) where four bands can be clearly discerned located at 1558, 1520, 1370 and 1331 cm −1 . Those detected at 1520 and 1331 cm −1 have been previously attributed to bidentate carbonates [ 49 , 50 ], whereas those located at 1558 and 1370 cm −1 can be assigned to bidentate formate species [ 51 ] adsorbed on ZrO 2 surface. The appearance of the latter bands is accompanied by evolution of three peaks in the ν (CO) region due to CO linearly adsorbed on reduced Ni sites (2021 cm −1 ) and bridged bonded CO (1909 and 1858 cm −1 ) [ 43 , 46 , 52 , 53 , 54 ].…”

The Effect of Shape-Controlled Pt and Pd Nanoparticles on Selective Catalytic Hydrodechlorination of Trichloroethylene

“…The surface adsorption sites present on the NPs were examined by infrared spectroscopy using CO as probe molecule [84][85][86][87][88][89][90][91][92][93]. All FTIR data were acquired after pretreatment (described in the Methods Section), in order to remove organic synthesis residues from the particle surfaces (which did not change the NP shapes; see the Supplementary Materials).…”