Characterization of Mo/C Catalysts by XRD, XPS, and TOF-SIMS

Abstract

A series of Mo/C catalysts were prepared by equilibrium adsorption of ( 4)6 7 24*4 20 onto a high surface area activated carbon. It was observed that the pH of the solution has a profound effect on the amount of Mo adsorbed on the carbon support. The Mo loading increases from ca. 0.2 to 14 wt % Mo as the pH of preparation decreases from 9 to 2. This behavior may be explained qualitatively in terms of electrostatic interactions between the molybdate ions and the protonated hydroxyl groups on the carbon surface. However, a detailed analysis of the results showed that other mechanisms which could include the participation of neutral hydroxyls may contribute to the adsorption process. The surface and bulk structure of the Mo/C catalysts were examined by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and X-ray diffraction (XRD). XRD and XPS intensity results indicated the presence of a highly dispersed monolayer-like Mo phase. TOF-SIMS and XPS valence band measurements showed that the catalysts contain polymeric Mo species at all loadings. This result was consistent with the predicted speciation based on the Mo solution chemistry and the point of zero charge of the catalysts.

Sorption of copper (II) and sulphate to different biochars before and after composting with farmyard manure

“…Biochar from flash pyrolysis sorbed little SO 4 ‐S (Figure S2). Sulphate sorption to charcoal and gasification coke strongly increased at the two largest concentrations of CuSO 4 addition, most probably as a consequence of reduced pH values, as shown for molybdate sorption to activated carbon (Rondon et al , 1995; Figures S1 and S2). We therefore focused on SO 4 ‐S sorption observed for the five smallest CuSO 4 concentration ranges (Figure 2).…”

Surface characterization of Pd/Al2O3sorbents for mercury capture from fuel gas

“…It has been demonstrated that XPS can be used for monitoring the dispersion of metals as a function of metal loading on supported catalysts [5][6][7][8]. Those studies showed that information about dispersion obtained by using XPS can then be correlated with catalytic activity.…”

“…The XPS metal-to-support intensity ratio will be proportional to the metal-to-support atomic ratio if the supported metal is dispersed as a monolayer. A thorough discussion of the model and some selected applications to supported catalysts are described elsewhere [5][6][7][8][9]. Some small modifications were made in the application of the K-M model for the calculation of the Pd/Al intensity ratios for monolayer coverage.…”

Static secondary ion mass spectrometry (S-SIMS) Part 2: material science applications

“…A series of Mo/C catalysts prepared with different Mo loadings (0.2±14 wt. %), and therefore at different pH values, were characterized by Rondon et al (1995). Fingerprints distinguished monomeric and polymeric Mo species.…”