Ammonia formation over Pd/Al2O3 modified with cerium and barium

We report experimental results for ammonia formation from nitric oxide and either a direct source of hydrogen or from a mixture of carbon monoxide and water over palladium based catalysts. Specifically, the addition of barium or cerium into an alumina supported palladium sample was studied. Static and transient flow reactor experiments were performed in order to identify the effects of temperature and the presence of oxygen on the activity for ammonia formation. Modification of Pd/Al2O3 with cerium proved to be beneficial for the activity due mainly to its enhancement of the water-gas-shift reaction, thus providing a higher availability of hydrogen for ammonia formation, but also because it remains active in the presence of slightly oxidizing global conditions when hydrogen is provided directly to the feed. Although the modification of Pd/Al2O3 with barium did not affect the ammonia formation during static conditions, the activity during lean/rich cycling increased. This is important for applications of passive selective catalytic reduction

Aspects of reducing agent and role of amine species in the reduction of NO over H-ZSM-5 in oxygen excess

In this study the selective catalytic reduction (SCR) of NO has been investigated over H-ZSM-5 with three different reducing agents. Comparison of the reaction mechanisms using propane, ammonia and isopropylamine has been performed using in situ DRIFTS step-response experiments. The same type of surface NH species, likely organic amines, is formed in the presence of either propane or isopropylamine as reducing agent. For NH3, on the other hand, NH4+ is the dominating NH surface species during reaction. Furthermore, in the case of propane, the nature of the NOx-source, i.e. NO or NO2, is crucial for the reaction. With NO2. the reaction likely proceeds fast via direct reduction, while for NO, oxidation to NO2 is required initially. in either case NH species play a vital role in the SCR reaction and organic amines are possible key-intermediates in the SCR with saturated hydrocarbons over H-ZSM-5

An investigation of the reaction mechanism for the promotion of propane oxidation over Pt/Al2O3 by SO2

Total oxidation of propane with oxygen in the absence and the respective presence of SO2 in the feed gas was studied over 1 wt% Pt on gamma -Al2O3 using transient experiments with TAP (temporal analysis of products) and in situ DRIFT spectroscopy. The TAP experiments confirm the promoting role of SO2 on the conversion of propane and, moreover, show an inhibiting effect from SO2 on the conversion of the intermediate products propene and CO. In situ DRIFT spectroscopy reveals the formation of sulphate species on the catalyst surface and indicates the formation of an allylic intermediate in the absence of SO2 only. Interaction between hydrocarbon intermediates and the sulphate species is confirmed by the appearance of thiol fragments in the mass spectra. The transient experiments show that propane in the first step is irreversibly adsorbed at the surface. Analysis of the surface residence times of the products formed at the propane pulse in pump-probe experiments provides information about the reaction pathways. Without S02 in the feed gas, propane reacts consecutively in the sequence propane --> propene -->. ethane --> CO --> CO2. In the presence of SO2 the first step of the main route is the breaking of a C-C bond in propane producing ethane and a C-1 fragment, which then form CO and eventually CO2. It is suggested that the promoting effect by SO2 on the conversion of propane is due to the formation of an acidic site at the Pt/Al2O3/SO42- interface. (C) 2001 Academic Press

Effect of silver loading on the lean NOx reduction with methanol over Ag-Al2O3

The influence of silver loading on the lean NO x reduction activity using methanol as reductant has been studied for alumina supported silver catalysts. In general, increasing the silver loading (0-3 wt%), in Ag-Al 2 O 3 , shifts or extends the activity window, for lean NO x reduction towards lower temperatures. In particular Ag-Al 2 O 3 with 3 wt% silver is active for NO x reduction under methanol-SCR conditions in a broad temperature interval (200-500 C), with high activity in the low temperature range (maximum around 300 C) typical for exhaust gases from diesel and other lean burn engines. Furthermore, increasing the C/N molar ratio enhances the reduction of NO x . However, too high C/N ratios results in poor selectivity to N 2 . \ua9 2013 Springer Science+Business Media New York