Palladium in Heterogeneous Oxidation Catalysis

Background

Palladium (Pd) is a silvery-shining metal discovered in 1803 by W.H. Wollastone. It is a member of the nickel group standing in group 10 (Ni, Pd, Pt) of the periodic table of elements and it is also a part of the platinum group metals (PGM) together with platinum, rhodium, ruthenium, iridium and osmium.

In general, metallic Pd and Pd ores are rare and often found together with other PGMs (e.g. alloyed with gold or platinum). However, the most commercial sources are deposits containing nickel and copper. The total Pd supply in 2012 was ca. 6.5 million oz.; 44% were extracted from Russian mines, 36% in South Africa (Johnson Matthey, 2014; Stillwater Palladium, 2012). Other important producing regions are located in North America and Africa; Figure 1 depicts the shares of the four largest producing countries. In addition, Pd is also obtained from recycling of noble metal containing scrap, mainly catalytic converters from automobiles.

Figure 1.

Palladium supply (%) by regions (Johnson Matthey, 2014)

Most of the Pd is used for automotive catalysts (65%), electronic, dental and jewelry application consume ca. 20%, the remaining part is for investment and other applications including its use as catalysts or dopants in catalyst formulations (Figure 2) (Manhattan Gold & Silver, 2011). In automotive catalysts, it is combined with platinum or rhodium and removes over 90% of harmful carbon monoxide, unconverted hydrocarbons and nitrogen oxides into water vapor, nitrogen and carbon dioxide. Pd plays also a key role in fuel cell technology to produce electricity and heat.

Figure 2.

Palladium demand (%) by application fields; AC = Automotive catalysts, E = Electronics, D = Dental, I = Investment and J = Jewelry (Johnson Matthey, 2014)