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EHC 226: Palladium
34
Table 8. Western world palladium metal demand according to application
a
Use
Deman
d
(tonnes)
(1993)
b
%
(1993)
Demand
(tonnes)
(1996)
c
% 
(1996)
Demand
(tonnes)
(1998)
c
%
(1998)
Electrical
equipment
61.1
45.0
64.1
31.9
64.4
24.8
Dental 
37.6
27.7
40.7
20.3
38.3
14.7
Automotive
emission
control
catalysts
20.3
(+3.2)
17.3
71.9
(+4.5)
38.1
139
53.4
Other
(catalysts,
jewellery,
chemicals)
13.5
9.9
17.6
8.8
18.5
7.1
Western sales
to China
–
–
1.9
0.9
–
–
Total
135.7
99.9
200.7
a
 
Comprises primary and refined secondary materials. Numbers in
parentheses represent the quantity of palladium recovered from the
automobile catalyst industry (internal cycle).
b
 
Adapted from Kroschwitz (1996).
c
 
Adapted from Cowley (1997, 1999).
such as very small multilayer ceramic capacitors, thick film resistors or
conductors.
Silver–palladium  alloys  are  used  for  electrical  contacts, and other
palladium alloys are used for electrical relays and switching systems in
telecommunication  equipment.  In  low-current technology, electrical
contacts  of  palladium  and  its  alloys  are used. Large numbers of so-
called  reed  contacts  (silver–palladium-, rhodium- or ruthenium-coated
contacts)  have  been  used  in  telephone  relays. Palladium can sometimes
replace  gold  in  coatings for electronics, electrical connectors and lead
frames  of  semiconductors  (Kroschwitz,  1996).  The  plating solutions
contain  palladium(II)  diamminedinitrite [Pd(NH
3
)
2
(NO
2
)
2
],  the  tetra-
ammine  complex  or  palladium(II)  chloride (Smith et al., 1978; Renner,
1992; Kroschwitz, 1996).

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Sources of Human and Environmental Exposure
35
3.2.3.2
Dental materials and other medical materials
Palladium  has  major  importance  in  dentistry   in  both  cast  and  direct
fillings.  Palladium  is  a  component  of  some  dental  amalgams .  Dental
casting gold alloys containing PGMs have been considered the
standard  material  for  all  types   of  cast  restorations.  Palladium   a l l o y s
(gold–silver–copper–PGM)  can  be  matched  to  any  dental application
(inlays,  full-cast crowns, long-span bridges, ceramic metal systems and
removable partial dentures) by small variations of the alloy compo-
sition  (Stümke, 1992). For example, there are more than 90 existing
palladium  alloys,  with  more  than  50%  in  Germany  for  fixed  restorations
with  ceramic  veneer (Zinke, 1992; Daunderer, 1993). However, in
Germany, dentists have recently been advised not to use palladium–
copper  alloys  unless  the  alloys  have  been  previously tested for corro-
sion resistance and biocompatibility (Zinke, 1992; BGA, 1993).
Recently, 
103
Pd  has  been  used  for  cancer  (e.g.,  prostrate)  brachy-
therapy,  a  form  of  cancer  radiation  therapy in which radioactive
sources  are  implanted  directly  into  a  malignant  tumour  (Sharkey  et  al.,
1998; Finger et al., 1999).
3.2.3.3
Automobile exhaust catalysts 
For  more  than  20  years,  automobile exhaust catalysts have been
used  to  reduce  levels  of  nitrogen  oxides, carbon monoxide and hydro-
carbons  in  automobile  exhausts.  In  the  last few years, catalysts
employing  precious  metal  combinations of platinum or palladium and
rhodium  in  a  ratio  of  5  to  1  (1.4–1.8  g  PGM/litre  catalyst  volume)  have
been  developed successfully (Abthoff et al., 1994; Degussa, 1995;
Kroschwitz,  1996).  Exhaust  gas  purificat ion  by  equipping  of  passenger
car  diesel  engines  with  palladium  oxidation  catalysts  has  been
achieved  only  since  about  1989  (Fabri  et  al.,  1990),  but  more  recent
information shows that palladium is not used on diesel vehicles, which
account  for  around  23%  of  the  European  market  (Cowley,  1997).
Concentrations  of  the  precious metals vary and depend upon the
specifications of the manufacturer (IPCS, 1991). Much of this
information is proprietary.
Worldwide  demand  for palladium in automobile catalysts rose
from  23.5  tonnes  in  1993  tonnes  to  76.4  tonnes  in  1996  (see  Table 8).
Around  60%  of  European  gasoline  cars  sold in 1997 were equipped
with  palladium-based  catalysts.  North  American  car  makers continued

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EHC 226: Palladium
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to  use  platinum-rich  underbody  catalysts,  but  there was increasing use
of  palladium starter catalysts to meet the hydrocarbon limits imposed
by  low-emission  vehicle  legislation. Many Japanese cars are equipped
with  palladium  systems,  whereas  platinum-rich  technology   remains
dominant elsewhere in Asia (Cowley, 1997).
3.2.3.4
Catalysts in chemical processes
Palladium has a strong catalytic activity for hydrogenation, dehy-
drogenation,  oxidation  and  hydrogenolysis  reactions.  Industrial  palla-
dium catalysts are in the form of finely divided powder, wire or gauze
or supported on substrates such as activated carbon, gamma-
aluminium  oxide  or  aluminium  silicates.  Often,  two  or  more  PGMs  are
combined  (Table  9).  In  the  petroleum  industry,  PGM   catalysts are used
to  produce  gasolines  with  high  antiknock  properties.  Palladium(II)
chloride  and  tetrachloropalladic(II)  acid are important homogeneous
catalysts  used  in the large-scale oxidation of ethylene to acetaldehyde
in  the  Wacker  process.  Palladium  catalysts are also used for the
acetoxylation  of  ethylene  to  vinyl  acetate  (Fishbein,  1976)  and in the
manufacture  of  sulfuric  acid  and methanol (Smith et al., 1978;
Kroschwitz, 1996).
Table 9. Examples of the catalytic activity of palladium
a
Principal
metal
Additional
metal
Reaction
Pt, Pd, Ir
Au 
oxidative dehydrogenation of alkanes, n-butene
to butadiene, methanol to formaldehyde,
dehydrogenation of alkylcyclohexanes,
isomerization and dehydrogenation of
alkylcyclohexanes or alkylcyclopentanes,
hydrogenative cleavage of alkanes,
dealkylation of alkylaromatics
Pd (powder
form)
Sn, Zn, Pb
selective hydrogenation of alkynes to alkanes
Pd
Ni, Rh, Ag
alkane dehydrogenation and dehydro-
cyclization
a
  Adapted from Renner (1992).
3.2.3.5
Fine jewellery and (optical) instruments
The use of palladium for jewellery, coinage and investment has
recently  begun on a small scale (“white gold”). Palladium’s major role
in  jewellery  fabrication  is  as  a  subsidiary  alloying component of the

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