Martin J. Fay

The adsorption of metal oxyanions on alumina

The adsorption of perrhenate, permanganate, molybdate, tungstate, and chromate on alumina was studied at pH 4.5. The effect of nitrate in the impregnation solution on the adsorption of these ions was examined as well as the effect of washing the freshly prepared catalysts. The uptake of perrhenate and permanganate decreased with increasing nitrate in the impregnation solution; the uptake of molybdate, tungstate, and chromate was unaffected. Washing the catalysts almost completely removed perrhenate, permanganate, and chromate, but allowed a significant amount of molybdate and tungstate to remain on the alumina. It is concluded that tungstate and molybdate adsorb on two types of surface sites, producing loosely and tightly bound surface species. From the amounts of molybdate and tungstate adsorbed, and from EXAFS results from washed and unwashed Mo/Al2O3 samples, both loosely and tightly bound molybdate and tungstate are polymeric in nature. The results are discussed in terms of electrostatic and surface reaction models.

EXAFS Smoothline Determination Using Splines: Finding the Optimal Smoothline and Fast Computation

The feasibility of the PC IMSL cubic spline smoothing routine CSSMH (ICSSCU in the mainframe edition) for numerical determination of the EXAFS smoothline (μo) is discussed. Examination of the cubic spline algorithm employed suggests that a relatively simple coding modification results in a considerably more efficient algorithm for use in EXAFS. The rudimentatary code already exists in the literature. This allows incorporation of the modified code into current programs without the large memory overhead necessary when IMSL is being used. The degree of flexibility is determined by a parameter which can have values in the range 0 to 1. The EXAFS smoothline requires that the algorithm be used at one extreme end of this range of flexibility. At the other end of this range the routine can be used for interpolation. A suggested path for finding the optimal smoothline, based on the use of coarse and fine smoothing parameters, is discussed.

Characterization of boron-modified Co/Al2O3 catalysts by EXAFS spectroscopy

EXAFS spectroscopy has been used to examine the effect of boron on the structure of Co/Al2O3 catalysts. The EXAFS results from unmodified Co/Al2O3 catalysts indicated that Co3O4 was formed at Co loadings of 1.5 wt % Co and higher. The lowest-loading (0.7 wt % Co) catalyst showed evidence of both tetrahedral and octahedral Co surface species. Modification of the Co/Al2O3 catalysts with 3 wt % B completely suppressed the formation of Co3O4 for Co loadings of 6 wt % Co and lower. In the absence of Co3O4, the Co species formed on the 3 wt % boron-modified catalysts were in a highly disordered state with large first shell Co-O coordinations and large Co-O nearest-neighbor distances. Results from a constant Co loading series (3 wt % Co) indicated that Co3O4 formation decreased as the boron loading increased. The distribution of supported Co species determined by EXAFS was compared with previous characterization by ESCA and gravimetric measurements; good agreement was found. A two-phase procedure was used to analyze the EXAFS data from the Co/B/Al2O3 catalysts. This two-phase analysis considered both the fraction of Co EXAFS from bulk Co oxide (Co3O4) and the remaining fraction from Co surface species. This allowed the amount of Co3O4 to be determined quantitatively and enabled structural information to be obtained from the Co surface phase.

Quantitative Characterization of Fe/Al2O3 Catalysts. Part I: Oxidic Precursors

The structure of a series of Fe/Al2O3 catalysts containing from 1 to 24 weight percent iron has been examined by XRD, EXAFS, Mössbauer, ESCA, and gravimetric analysis. Two iron phases, Fe2O3 and Fe+3 in solid solution in the alumina support, are characterized as a function of iron loading. The combination of ESCA H2 titration and gravimetric analysis allows both quantitative and qualitative measurement of the two species. The amount of Fe2O3 phase increases with increasing iron loading for Fe1 to Fe24, whereas the amount of Fe+3 solid-solution phase increases with increasing iron loading for Fe1 to Fe6 and then levels off to approximately 2.2 wt % Fe for Fe8 to Fe24. The particle size of the Fe2O3 phase, determined from ESCA measurements, increases with increasing iron loading.

Application of cross-correlation analysis to EXAFS: Investigation of the cobalt phase on boron modified cobalt/alumina catalysts

Boron modified Co/Al2O3 catalysts, previously characterized by ESCA, are examined by EXAFS. A method of data analysis based on cross-correlation of the χ(E) spectra is used to determine the relative amounts of Co3O4 and cobalt surface phase present on the catalysts. The results are compared with those obtained previously by ESCA. The EXAFS analysis agrees well with the ESCA results. No gas-phase reactions were required to elucidate the relative proportion of cobalt species by EXAFS as is necessary for the ESCA analysis.

EXAFS characterization of Ti/Al2O3 supports and Co/Ti/Al2O3 catalysts

The structure of Ti/Al2O3 supports (0–14 wt% Ti) and Co/Ti/Al2O3 catalysts (3 wt% Co) was examined by EXAFS. The results indicated that the Ti was present primarily as a highly dispersed surface phase. The Ti EXAFS results indicated that the Ti species were octahedrally coordinated. Evidence of Ti—Ti interactions was found for all loadings (2–14 wt% Ti) suggesting that the Ti surface species are present as small clusters of TiO2.The Co EXAFS results showed evidence for several structurally different Co surface phases as a function of Ti loading. Evidence of a Co species interacting with the Ti surface phase was observed for the 3% Co/2% Ti-3%Co/6%Ti catalysts. At the highest loadings studied, 3%Co/8%Ti and 3%Co/14%Ti, evidence was found for a CoTiO3-like phase.