The influence of particle size on CO adsorption on Pd/alumina model catalysts

Kinetics of CO oxidation on palladium using microkinetics coupled with reaction route analysis

“…On the other hand, DFT model predictions (Zhang and Hu, 2001), propose a value of 1.6 eV (1 eV = 23.06 kcal/mol) for adsorption of CO on pre-adsorbed O on Pd (111). Similar energy predictions were also obtained from the DFT studies by Martin et al (2014) proposing a range of values from 1.82 eV-1.75 eV for CO adsorption on different adsorption sites on clean Pd (111).The equivalent range of chemisorption energy for CO adsorption has also been reported (Eichler, 2002;Zorn et al, 2011).This chemisorption energy of 34 kcal/mol is in good agreement with the ϭϱ experimental results (Engel and Ertl, 1979;Chou and Vannice, 1987a) and UHV studies (Szanyi et al, 1993;Stara and Matolin, 1994) on clean Pd (111). However, calorimetric studies (Conrad et al, 1974;Peter et al, 2013a) suggest coverage dependent activation energies for CO desorption on Pd (111). Conrad et al (1974) observed a constant value of CO desorption energy till coverage of 0.33 and then decreasing to 20 kcal/mol at higher coverages.…”

Particle-size dependent heats of adsorption of CO on supported Pd nanoparticles as measured with a single-crystal microcalorimeter

“…This is an exceptionally important question that lies at the very heart of understanding particle size effects in catalysis. 1 The energetics of interaction of gaseous molecules, particularly carbon monoxide, with well-defined metal nanoparticles were previously addressed indirectly in nonisothermal temperature-programed desorption ͑TPD͒ experiments 2 and in isothermal modulated molecular-beam studies, 3 where the adsorption energies were obtained by modeling the desorption process and analyzing the lifetimes of the adsorbate on the surface. However, these indirect methods did not provide a clear trend in the changes in the adsorption energy with the particles size: whereas the TPD studies found a decrease in the adsorption energy by about 10 kJ mol −1 on the 2.5 nm sized Pd particles as compared to the extended single-crystal surfaces, the kinetic model used for analysis of the molecular-beam experiments predicted a pronounced increase in the adsorption energy by about 35 kJ mol −1 on the particles smaller than 1.5 nm.…”

Size-dependent properties of transition metal clusters: from molecules to crystals and surfaces – computational studies with the program ParaGauss

“…Being able to determine palladium NPs with the lowest adsorption energy is important for catalysis because, according to the Sabatier principle, these systems potentially exhibit the highest reaction rates. 20,254 To examine computationally this discrepancy between different sets of experiments, 20,253-255 the CO adsorption energies at threefold hollow sites of a variety of small to medium-sized Pd n clusters were calculated 22 (using the RPBE 246 functional). 253,255 The aforementioned MB experiments detected this minimum at a particle diameter d eff E 5 nm.…”