According to a Reuters story this week, Mitsui Mining and Smelting Co. Ltd. said it has developed a new catalyst for diesel engine cars that replaces the use of platinum with silver.
I began this morning going over the (U.S.) Mitsui patents on exhaust emission catalysts. They begin in 1973 with the issuance of a patent to Mitsui's Asahi Chemical; the research for which must have begun in the late 1960s for a silver based catalyst for reducing nitrogen oxides and carbon monoxide. There is a hiatus of about a decade, and a steady stream of patents, citing that first one, beginning in the 1990s.
The original focus of the work was to reduce nitrogen oxides and sulfur oxides (the acid rain formers, the first being from gasoline powered cars, and the second mostly produced by diesels) to nitrogen and, I guess, sulfur, which would then be necessary to filter out. In any case this was not the direction that early workers, myself included, took.
The problem was carbon monoxide and unburned fuel, and it was solved by platinum and palladium continuous coatings on the surface of alumina beads packed between two stainless steel screens in a 'can' inserted at the exhaust manifold to achieve maximum temperature as quickly as possible (i.e., the so-called catalytic converter).
I could go on, and I probably will next week, about my friend Dan Shanefield's discovery of a process for the mass production of the synthetic cordierite substrate, and the emphasis on reducing acid-rain forming emissions from vehicles that took place in the late 1970s.
The solution then was rhodium; it was quick, relatively cheap - it utilized an almost useless byproduct of platinum mining and the South Africans loved the idea - and it was available. Asahi Chemical couldn't get a foothold in the business. Japanese car making clout was just too small at the time, and the Japanese car makers feared the regulators of their temporary masters and their European running dogs.
Reuters really seems to have gotten the story wrong. The major problem with diesel emission control is the mandate for the dramatic reduction of nitrogen (and sulfur) oxides. Mitsui is going after the rhodium used today in selective catalytic reduction (SCR), an expensive mandatory add on that reduces the amount of rhodium (but by no means eliminates it) in a diesel exhaust emission management system.
I note also that a typical formulation includes a silver composition with a rare earth metal. This is a great story about a new driver for reducing rhodium demand and increasing rare earth demand. Who woulda thunk?
Stay tuned for next week's story: Driving Rhodium Consumption Down and Silver Consumption Up.