Structure and catalytic activity of alumina supported platinum-cobalt bimetallic catalysts. 3. Effect of treatment on the interface layer

Abstract

and bulk concentration (e) can be determined from the semiintegration of a single voltammogram. The approach is illustrated using p-benzoquinone (pBQ) where the adsorption and diffusion response are indistinguishable, characteristic of weak adsorption. A surface ex-of 3 nmol/cm2 was determined via semiintegration and confirmed using chronocoulometry. Advantages and disadvantages of the method relative to chronocoulometry are discussed. The semiintegral analysis approach is extended to cases where the elwtrcdc surface is covered by a thin film where the thickness is sufficiently small so that mass transfer within the Nm is not significant (Le., thickness << (mz)lI2). heoncentration of redox species in the f h will rcpUlt in an apparent initial surface excess, similar to adsorption.When the film is in contact with species in solution, the response will contain diffusional and nondiffusional components, analogous to the response observed for adsorption in the prcaence of species in solution. Simulations are used to demonstrate that semiintegral analysis may be used to determine the concentration within the film and partitioning coefficients of species between the bulk and the film.

Metal−Support Interactions in Co/Al2O3 Catalysts: A Comparative Study on Reactivity of Support

“…XPS analytical results on Co 2p 3/2 binding energies are presented in Table 1, followed by the literature data of various Co-containing compounds in Table 2. 16 As can be seen, the Co 2p 3/2 component at 779.3 eV indicates that the surface cobalt is largely present as Co 3 O 4 in the IM1 sample. The other component at 781.4 eV cannot be assigned to bulk CoAl 2 O 4 because there is no shake-up satellite observed (Table 2) and low reactivity in the commercial γ-Al 2 O 3 support is generally expected.…”

“…2,7,16 For a similar reason, the second peak at 782.3 eV cannot be assigned to CSP but to CoAl 2 O 4 , since stronger satellites for both CoO and CoAl 2 O 4 are also observed in this sample. 16 Chemical Reactivity of Catalysts. H 2 -TPR (TGA) results for the three catalyst samples are presented in Figure 4.…”

“…Nevertheless, this component can be attributed to a cobalt surface phase (CSP), as assigned in the catalyst system using a similar impregnation method with a 3 The CSP phase was believed to cover over the alumina support during the calcination and it is a hardly reducible surface phase. [16][17][18] In the absence of solidstate diffusion into the support matrix, this surface phase is highly dispersed and is presumably present in the monolayer thickness. [16][17][18] For the IM2, the Co 2p 3/2 peaks are accompanied by strong shake-up satellites.…”

“…The peak at BE ) 780.0 eV is the characteristic of cobalt monoxide CoO, because CoO, rather than Co 3 O 4 , has a strong shake-up satellite peak 5 eV higher than its main peak and has a spin-orbit coupling of around 15.5 eV (Tables 1 and 2). 2,16 Another peak at BE ) 782.0 eV is assigned to CoAl 2 O 4 , since CoAl 2 O 4 also has a strong shakeup satellite at the energy 6 eV higher. 16 Similar to the IM2 sample, CoO is a surface component in the SG sample with its Co 2p 3/2 peak at 780.2 eV but with a much lower intensity, which indicates a strong interaction between the cobalt oxide and alumina.…”

“…2,16 Another peak at BE ) 782.0 eV is assigned to CoAl 2 O 4 , since CoAl 2 O 4 also has a strong shakeup satellite at the energy 6 eV higher. 16 Similar to the IM2 sample, CoO is a surface component in the SG sample with its Co 2p 3/2 peak at 780.2 eV but with a much lower intensity, which indicates a strong interaction between the cobalt oxide and alumina. 2,7,16 For a similar reason, the second peak at 782.3 eV cannot be assigned to CSP but to CoAl 2 O 4 , since stronger satellites for both CoO and CoAl 2 O 4 are also observed in this sample.…”