Kalle Arve

On the performance of Ag/Al2O3 as a HC-SCR catalyst – influence of silver loading, morphology and nature of the reductant

This study focuses on the performance of Ag/Al2O3 catalysts for hydrocarbon selective catalytic reduction (HC-SCR) of NOx under lean conditions, using complex hydrocarbons as reductants. The aim is to elucidate the correlation towards the silver loading and morphology, with respect to the nature of the reductant. Ag/Al2O3 samples with either 2 or 6 wt% silver loading were prepared, using a sol–gel method including freeze-drying. The catalytic performance of the samples was evaluated by flow reactor experiments, with paraffins, olefins and aromatics of different nature as reductants. The physiochemical properties of the samples were characterized by scanning electron microscopy/energy dispersive X-ray spectroscopy, scanning transmission electron microscopy/high angle annular dark field imaging, X-ray photoelectron spectroscopy and N2-physisorption. The 2 wt% Ag/Al2O3 sample was found to be the most active catalyst in terms of NOx reduction. However, the results from the activity studies revealed that the decisive factor for high activity at low temperatures is not only connected to the silver loading per se. There is also a strong correlation between the silver loading and morphology (i.e. the ratio between low- and high-coordinated silver atoms) and the nature of the hydrocarbon, on the activity for NOx reduction. Calculated reaction rates over the low-coordinated step and high-coordinated terrace sites showed that the morphology of silver has a significant role in the HC-SCR reaction. For applications which include complex hydrocarbons as reductants (e.g. diesel), these issues need to be considered when designing highly active catalysts.

Deposition of carbonaceous species over Ag/alumina catalysts for the HC-SCR of NOx under lean conditions: a qualitative and quantitative study

The deposition of carbonaceous species on fresh and aged Ag/Al2O3 catalysts used for the selective catalytic reduction of NOx (HC-SCR) was investigated by a combination of analytical techniques including SEM-EDXA, nitrogen physisorption, GC-MS and TGA. Time-on-stream (TOS) experiments were carried out to determine the level of deactivation over the catalysts. Short-term deactivation was monitored with a MicroGC with a short retention time. In addition, long-term deactivation was also investigated. Hexadecane, a paraffinic component that can be produced by decarboxylation and/or decarbonylation of natural oils and fats, and a standard Finnish commercial diesel fuel were used as the reducing agents. Finally, the influence of hydrogen on the carbonaceous deposition over the catalyst was also investigated. The NO-to-N2 activity improved in the temperature range 200–500 °C as hexadecane and H2 were used as reducing agents. In the case of commercial diesel fuel, a similar positive effect of H2 on the activity was also observed, however, at somewhat higher temperature, e.g., 350–500 °C. The results from the qualitative and quantitative analyses of the carbon deposits on the catalysts are presented and discussed. Indications of decreased activity over the catalyst were found, especially at low temperatures (<350 °C). Nevertheless, only small amounts of carbon were found on the catalytic surface. It is suggested that the deactivation phenomenon could not only be attributed to the deposition of carbonaceous species on the catalysts surface but the dependence of the adsorption kinetics of the reacting species as a function of temperature and partial pressure should also be carefully taken into account.

Chapter 3:Catalytic Hydrogenation of Sugars

Heterogeneous catalytic hydrogenation of various sugars over a range of catalysts was historically done mainly using sponge nickel catalysts, while more recently ruthenium based catalysts started to be applied since Ru affords good activity and excellent selectivity in addition to being void of the toxic properties of Ni. The chapter covers various aspects of catalytic sugar hydrogenations, such as catalyst selection, reaction kinetics, sugar structure influence, structure sensitivity and reactor design.

ANN modeling applied to NOX reduction with octane. Ann future in personal vehicles

A silver/alumina catalyst was tested for its NOX reduction activity during oxygen-rich conditions and during variation in the input parameters (nitric oxide, octane and oxygen). A multi-bed approach was tested where the initial bed was divided into four beds acting in different temperature rages. The experimental data were investigated by means of artificial neural networks that were demonstrated to be able to model the process.