A new method for the determination of the monolayer capacity for hydrogen on a metal supported catalyst based on thermodynamic criteria applied to the

Hydrogen and oxygen adsorption stoichiometries on silica supported ruthenium nanoparticles

“…Of various methods targeted at measuring particles dispersion measurements, H 2 and O 2 adsorptions [3] are very useful and convenient: however this approach relies on the knowledge of the number of hydrogen adsorbed per surface atoms, and this stoichiometric ratio depends on the metals. In the case of platinum [4,5] and rhodium, [6] extended studies on adsorption measurements, based on Langmuir adsorption isotherms, correlated to particle size distributions (determined by TEM), led to the stoichiometry of 2H/M s , in contrast to the former accepted value of 1H/M s . [7] In the case of ruthenium, early studies on Ru powders suggested a ratio of 1.5 by comparing H 2 and N 2 adsorptions.…”

Non‐Zeolitic Standard Catalysts

“…The most strongly held state is assigned to H spillover, and some of the H 2 ''chemisorbed'' is thought to be used to break Pt − O − Si bridges formed between the metal particles and the support. Three groups have reported heats of adsorption for H 2 [7,11], but the results are not in exact agreement. 1 H NMR has also been used to identify states of H 2 adsorption [4,7].…”

“…The process has been investigated with EUROPT-1 by several groups [4,7,11,12], with results that have general importance for the validity of the method. It has been widely assumed that surface stoichiometry H/Pt s may be taken as unity irrespective of particle size, despite evidence to the contrary with other metals.…”

“…The difficulty with the often-used ''extrapolation to zero pressure'' method for estimating monolayer volume is that the intercept increases as the pressure range is extended [11] and thus has no real significance. The data also seem to obey the Temkin equation over very wide pressure ranges [4,11], although the logarithmic form of the equation does not admit of a saturation limit. It is, however, concluded that in practice adsorption is complete at about 3.3 × 10 4 Pa pressure, the uptake being 200 µmol g −1 (H:Pt s = 1.24), with little further adsorption occurring up to 6.5 × 10 5 Pa pressure.…”