Catalysts & Petrochemicals

X-ray photoelectron spectroscopy is used to characterise materials and surfaces used as catalysts for numerous chemical reactions with great success. Surface studies of catalysts range from fundamental research into core level shifts induced by adsorbed species as a model of reaction intermediates to applied research on used industrially relevant catalysts.  Here we present a number of recent papers which include data acquired using Kratos AXIS spectrometers.


Non-lattice surface oxygen species implicated in the catalytic partial oxidation of decane to oxygenated aromatics

Sivaram Pradhan, Jonathan K. Bartley, Donald Bethell, Albert F. Carley, Marco Conte, Stan Golunski, Matthew P. House, Robert L. Jenkins, Rhys Lloyd and Graham J. Hutchings

Nat. Chem., 2012, 12, 134–139. DOI:10.1038/nchem.1245

The one-step transformation of C7–C12 linear alkanes into more valuable oxygenates provides heterogeneous catalysis with a major challenge. In evaluating the potential of a classic mixed-metal-oxide catalyst, we demonstrate new insights into the reactivity of adsorbed oxygen species. During the aerobic gas-phase conversion of n-decane over iron molybdate, the product distribution correlates with the condition of the catalyst. Selectivity to oxygenated aromatics peaks at 350°C while the catalyst is in a fully oxidized state, whereas decene and aromatic hydrocarbons dominate at higher temperatures. The high-temperature performance is consistent with an underlying redox mechanism in which lattice oxide ions abstract hydrogen from decane. At lower temperatures, the formation of oxygenated aromatics competes with the formation of CO2, implying that electrophilic adsorbed oxygen is involved in both reactions. We suggest, therefore, that so-called non-selective oxygen is capable of insertion into carbon-rich surface intermediates to generate aromatic partial oxidation products.

Active gold species on cerium oxide nanoshapes for methanol steam reforming and the water gas shift reactions

Nan Yi, Rui Si, Howard Saltsburg and Maria Flytzani-Stephanopoulos,

Energy Environ. Sci., 2010, 3, 831–837. DOI: 10.1039/B924051A

We report that a small amount (<1 at%) of gold on ceria single crystals prepared as nanorods (10 ± 2.8 by 50–200 nm) of {110} and {100} crystal surfaces shows excellent catalytic activity in both the steam reforming of methanol (SRM) and the water gas shift (WGS) reactions at low temperatures (<250°C). The ceria nanorods bind and stabilize gold as atoms and clusters (<1nm, TEM invisible). On the other hand, gold nanoparticles ( 3 nm) are found on the {100} surfaces of ceria nanocubes. Very low rates of SRM and WGS were measured on the Au–ceria {100} cubes, while the rates on Au–ceria {110} rods were at least an order of magnitude higher. However, the apparent activation energies did not depend on the shape of ceria. Strong bonded Aun–O–Ce species are the active sites and these are present only in negligible concentrations on the {100} surfaces. Thus, both reactions are structure-insensitive on Au–ceria. SRM proceeds through the methyl formate route. The Au–ceria {110} catalyst shows both high SRM activity and high selectivity to CO2 at temperatures below 250°C.