In situ XANES study of Mn in promoted sulfated zirconia catalysts

Mn-promoted sulfated zirconia catalysts (2 wt% Mn) were investigated in situ, during the catalyst activation, isomerization of n-butane, and subsequent re-activation, using X-ray absorption spectroscopy of the Mn K-edge. The average valence of Mn in the catalysts, as determined from the edge position, was found to change from either 2.65 or 2.77 in the calcined samples to about 2.5 during activation in He (703 K for 30 min). During the isomerization of n-butane (1% in He, 80 ml min-1, 0.5 g catalyst at 333 K), the average Mn valence did not change further. When the catalyst was activated in 50% O2 the average valence only decreased from about 2.78 to 2.72. In this case, the average valence during the isomerization reaction decreased at a nearly constant rate both during the induction of activity and deactivation of the catalyst. The data do not support a stoichiometric redox reaction involving the promoter as initiator of the isomerization. However, a higher Mn valence after activation was indicative of a higher maximum conversion. It is concluded that the promoter cations function through modification of the structure of the zirconia.     

In situ surface characterization of the intermetallic compound PdGa – A highly selective hydrogenation catalyst

The structurally well-defined intermetallic compound PdGa – a highly selective catalyst for the semi-hydrogenation of acetylene – was characterized by Fourier transform infrared spectroscopy (FTIR) in situ X-ray photoelectron spectroscopy and in situ prompt gamma activation analysis. A strong modification of the electronic states in PdGa compared to elemental Pd was revealed as well as the complete isolation of the Pd atoms on the surface of PdGa. In situ investigations proved the high stability of the surface, thus excluding segregation phenomena (common for alloys) or sub-surface chemistry involving C and/or H atoms (known for elemental Pd). By suppressing the sub-surface chemistry, the electronic modification as well as the site isolation lead to the high selectivity and long-term stability of PdGa in the semi-hydrogenation of acetylene.     

Investigation of the Hydrate Plugging and Non-Plugging Properties of Oils

Three laboratories (Norwegian Institute of Science and Technology [NTNU], Institut Français du Pétrole [IFP], and the Colorado School of Mines [CSM]) determined hydrate plug formation characteristics in three oils, each in three conditions: (1) in their natural state, (2) with asphaltenes removed, and (3) with naturally occurring acids removed from the oil. The objective was to determine the major variables that affect hydrate plugging tendencies in oil-dominated systems, to enable the flow assurance engineer to qualitatively assess the tendency of an oil to plug with hydrates. In the past, it was indicated that chemical effects, for example, water-in-oil/hydrate-in-oil (emulsion/dispersion) stability, prevented hydrate plugs. For example, deasphalted oils provided low emulsion/dispersion stability and thus hydrate particles aggregated. In contrast pH 14-extracted oils were reported to remove stabilizing naphthenic acids, causing asphaltene precipitation on water/hydrate droplets, stabilizing the emulsion/dispersion to prevent aggregation and pluggage. This work suggests that in addition to chemistry, shear can enable plug-free operation in the hydrate region. High shear can prevent hydrate particle aggregation, while low shear encourages particle aggregation and plugging. As a result, flow assurance engineers may be able to forecast hydrate plug liability of an oil by a combination of chemistry and flow variables, such as: a) measurements of live oil emulsion stability, b) predictions of flow line shear, and c) knowledge of water cut. Plug formation qualitative trends are provided for the above three variables. Implications for flow assurance are given.     

Catalytically active gold clusters and nanoparticles for CO oxidation

Electronic states of gold nanoparticles in mordenite and their transformations under redox treatments have been studied by the methods of FTIR spectroscopy of adsorbed CO and diffuse reflectance UV-visible spectroscopy. Different states of ionic and metallic gold were detected in the zeolite channels and on the external surface of the zeolite - Au⁺ and Au³⁺ ions, charged clusters , and neutral nanoparticles Au_m. Catalytic tests of the samples revealed the existence of two types of active sites of gold in CO oxidation - gold clusters <2 nm (low-temperature activity) and gold nanoparticles (high temperature activity).     

Silver as acrolein hydrogenation catalyst: intricate effects of catalyst nature and reactant partial pressures

The hydrogenation of acrolein over pure and supported silver has been investigated with a focus on the influence of catalyst structure and reaction pressure (mbar to 20 bar range) on activity and selectivity. An onset of formation of allyl alcohol beyond 100 mbar reaction pressure (at 250 degrees C) is ascribed to a change in adsorption geometry upon increasing coverage. Smaller silver particles (in the nanometer range), the proximity of a reducible oxide component as well as high pressure lead to enhanced allyl alcohol formation; the selectivity to the other main product propionaldehyde is reduced. The silver dispersion changed depending on the reaction pressure. Moreover, the presence of oxygen, most likely as subsurface oxygen, and the presence of defects are of paramount importance for the catalytic behaviour. The considerable changes of the silver catalysts under reaction conditions and the pressure dependence call for in situ measurements to establish true structure-activity/selectivity relationships for this system.