MKS precise: a holistic and tailor-made system approach
2010-07-19
Despite the application of best available recovery technology PGM losses can only be reduced to a certain extent. Substantial progress can be achieved by modified concepts for the platinum based catalyst reducing primary losses and consequently allowing a more economic utilization of the palladium based recovery system. Such a concept comprises a precise adjustment of the alloying components in the catalyst gauzes and their tailored sequence in the assembly as a third variable, apart from gauze structure and process wire size.
Various operating experiences accompanied by intensive research study have fundamentally modified the understanding of catalyst technology and its application in the ammonia oxidation process over the last ten years. The implementation of this knowledge in the use of varying gauze structures and processed wire sizes in customized catalyst assemblies originally increased rates of yield accompanied by lower initial applied PGM weight.
Less attention was paid to the primary precious metal losses from the catalyst since these were recovered to a certain extent by applying secondary methods such as palladium based recovery systems. Efforts to stabilize platinum by addition of various precious metals or metal-oxides impaired the catalyst activity and thus the rate of yield.
Umicore has tackled the route to make use of the ability of palladium to act as catalyst for the ammonia oxidation as well as the recovery system for platinum and rhodium. Applied together with platinum and rhodium in a tertiary catalyst alloy these characteristics are differentially expressed depending on the composition of the individual metals as well as the temperature and ageing behaviour in the different gauze layers in the gauze assembly.
 |
 |
|
|
Fig. 1: temperature sensitive selectivity |
Fig. 2: micrograph of an aged wire; performance of Pt/Rh/Pd in the distribution and accumulation |