Catalysts for Oxidation of Ammonia to Oxides of Nitrogen

Catalytic Oxidations of Inorganic and Organic Compounds

“…The first commercial plant was built in 1906 near Bochum, Germany, based on process and catalyst development by Ostwald (Wagner and Fetzer, 1997). The Pt-Rh catalyst was discovered in the 1930s at DuPont (Hansforth and Tilley, 1934), and with little modification was the catalyst of choice until the early 1990s. Presently, the catalyst of choice is an alloy composed of 90% Pt and 10% Rh configured in the form of a solid woven or knitted metal wire gauze; a woven gauze is shown in Figure 8.4.…”

The Historical Development of Catalytic Oxidation Processes

“…Both of these conditions were found to result in rapid deterioration of the catalyst and an accelerated loss of platinum from it. In fact the conditions necessary to operate efficiently in the ammonia burner at pressure would have involved quite unacceptable losses of platinum from the catalyst and costly, short catalyst lives, but for the development at EI Du Pont De Nemours and Co Inc, by Handforth and Tilley [143], of a platinum-rhodium alloy which suffered much reduced loss of metal. In developing this alloy they studied the phenomenon of platinum loss under ammonia oxidation conditions and found that the loss at a given temperature was proportional to the weight of oxygen in the gas mixture passed over the catalyst.…”

“…Superiority of PtjRh gauze over Pt gauze catalyst in ammonia oxidation [143] The better efficiency, reduced rate of loss and longer life have made this alloy the standard ammonia oxidation catalyst ever since and it is universally used in the form of gauze, normally of 80 mesh inch-1 with wire of 0.003 inch diameter. It is not too surprising that there have been no major developments in ammonia oxidation catalysts since, as these gauzes are capable of oxidising ammonia to nitric oxide at selectivities in excess of 94 % with a life of many months and with a level of platinum loss low enough to ensure that the platinum costs contribute only a few percent of the total plant operating costs.…”

Quick low temperature coalescence of Pt nanocrystals on silica exposed to NO – the case of reconstruction driven growth?

“…The suggested migrating species are volatile NOcontaining Pt complexes. This may add to the understanding of the experimental observation of weight loss of a platinum gauze during ammonia oxidation approaching a constant value at temperatures falling from 1170 K to 1000 K. 10 During ammonia oxidation, NO is an intermediate product interacting with O 2 and the catalyst. The loss occurs in an oxidizing environment and may resemble the weight loss of Pt foil heated in air, 11 attributed to volatile PtO 2 .…”