Metal-Catalysed Reactions of Hydrocarbons / 05-Introduction to the Catalysis of Hydrocarbon Reactions

flow-rate of either reactant will have consequences that can give kinetic/ mechanistic information, and the replacement of one reactant by an isotopic variant is perhaps the best way of all because then there is no change in surface conditions, so that the emergence of a labelled product reflects the actual surface concentrations (Figure 5.16). Deuterium and tritium are not however suitable labels, as their atoms are very mobile as we shall see in the following chapter. 13C is much to be preferred.

A further advance is the TAP (Temporal Analysis of Products) reactor, where very fast reaction steps can be followed, but the equipment needed is sophisticated, and has not been much used for reactions of interest to us. Catalytic reactions can also be run in an infrared spectrometer cell, so that adsorbed species can be inspected after if not during reaction. Finally reactions can now readily be performed inside UHV apparatus, so that detailed knowledge of the state of the surface single crystals during and after reaction is accessible.13,107

Heterogeneous catalysis is a subject full of surprises, and one of these, long known but never completely explained, is the difference sometimes observed between the kinetic laws derived from constant volume reactors, (a) by following the change of rate with time, and (b) by observing the effect of changing reactant pressures on initial rate. A specific case in point is the hydrogenation of ethyne and other alkynes, where with hydrogen/alkyne ratios exceeding two, the time-order is accurate zero, i.e. the rate stays the same for much of the reaction, whereas the pressure-order is approximately first;108,109 and moreover a sudden change in hydrogen pressure alters the rate.110,111 This does not happen when the hydrogen/alkyne ratio is below two. It seems possible that in the former condition a self-sustaining surface chain reaction is set up (see Chapter 10).

5.8.2. Use of Stable and Radioactive Isotopes112 –115

The discovery of deuterium by H.C. Urey in 1932 was seized upon by physical chemists interested in kinetics and mechanism, and indeed proved a godsend to students of heterogeneous catalysis, where it quickly revealed a wealth of unexpected subtlety and complexity in the mechanism of hydrocarbon reactions catalysed by metals. H.S. Taylor’s laboratory at Princeton was the first to prepare heavy water (D2O) by electrolysis,116 but the first publications on the use of deuterium in hydrogenation came in 1934 from Manchester and Cambridge, where it was shown that in the reaction with ethene the deuterium content of the non-condensable fraction fell, so that an exchange reaction was taking place117,18 (Chapter 7). Product analysis was at this time limited to thermal conductivity, and recognition of the composition of the ethene and the ethane had to await the arrival of analytical mass-spectrometry in about 1950. Infrared spectroscopy also made a useful contribution, for example in analysing mixtures of C2H2, C2HD and C2D2,

250 CHAPTER 5

and of the positional isomers of C2H2D2.119,120 Taylor’s laboratory also made the first measurements of the metal-catalysed exchange of alkanes with deuterium121 (Chapter 6).

The early analytical use of mass spectrometry was difficult and tedious, as when examining the reaction of ethene with deuterium it was necessary to remove ethene by chemical absorption from a small sample of product in order to obtain the mass spectrum of the ethane fraction, and then to derive the spectrum of the ethene by difference between this and the untreated sample.122 Obtaining the actual composition from the raw data was also troublesome because the ethane parent ion C2X6+ (X = H or D) readily loses X2 to form C2X4+, and before the advent of the computer there was a tiresome calculation to be performed, involving correction for 13C natural impurities and the presence of fragment ions. The extent of fragmentation (less with ethene and with propane than with ethane) decreases at low ionising voltage as the appearance potential of the fragment is approached, but in the case of ethane this is actually below the ionisation potential of the parent ion, so fragmentation is unavoidable.123 Operating a mass-spectrometer at the necessary low ionising voltage of 12V was at that time a somewhat risky undertaking. The advent of preparative gas chromatography simplified the analytical procedure greatly, and then it was possible to observe the inclusion of deuterium atoms into each of the three n-butene isomers, as well as into the n-butene, in the reaction of l-butene with deuterium124 (Chapter 7).

Mass-spectrometry does not however report the position of a deuterium atom in a hydrocarbon molecule (i.e. it cannot distinguish CH2D-CH2D from CH3- CHD2) except by analysis of the fragment ions, which is neither easy nor reliable.125 NMR has however come to the rescue and has been of great use in providing further detail of mechanical routes.126 Microwave spectroscopy has distinguished the isotopomers of propene and of 1-butene and E -2-butene.13,125 High-resolution mass-spectrometry is however now able to separate ions of nominally the same mass, thus avoiding the problem of subtraction of fragment ion currents: so for example separation of the ions C2H6+, C2H4D+, C2H2D2+ and C2D4+ in the mass range 30.040–30.048 has been achieved.

We end with a word on nomenclature. First, as to reactions: where deuterium is substituted for hydrogen, as say in its reaction with methane, we may speak of exchange or better of equilibration of the mixture. In the reaction with ethene, deuterated ethenes are formed by exchange or deuteriation because there is no time for them to equilibrate: the process of addition to the CC bond is sometimes called deuteriumation (logically correct, but inelegant) or deuterogenation (logically incorrect and even more unpleasant). The location of deuterium atoms can be expressed by using the Boughton convention, by which for example CH2D- CH2D becomes ethane-1,2-d2 and CH3-CHD2 is ethane-1,1-d2. This terminology has certain merits that will appear later.

Figure 5.17. Use of 13 C-labelled 2-methylpentane to distinguish bond-shift and cyclic intermediate mechanisms for isomerisation to 3-methylpentane.

Tritium is a weak β− emitter127–130 (Emax, 18.6 keV) and has seen some use in chemisorption and catalysis of hydrocarbon reactions: its location in a hydrocarbon molecule can be formed by NMR spectroscopy.131 The 14C carbon isotope (Emax,155 keV) has been successfully used to monitor chemisorption of labelled hydrocarbons and to assess the importance of final product formation from an intermediate product.132 Thus for example in the reaction Scheme 5.1, addition of labelled X during the reaction and measurement of the activity in the product Z allows the importance of the re-adsorption of gaseous X to be estimated.131 13C has played an important role in the work of Fran¸cois Gault and his associates in determining mechanisms of skeletal isomerisation of hydrocarbons75,133 (see Chapter 14). The power of this technique can be simply illustrated by comparing the products formed by isomerising 2-methylpentane by alternative mechanisms (see Figure 5.17). 3-Methylpentane is formed by each route, but only the position of the label reveals the route involved. Very often both mechanisms operate simultaneously, and for details of the elegant but tedious way in which the product is degraded chemically to show how much of the label is in each place, references 75 and 133 should be consulted.

REFERENCES

1.J.M. Thomas and W.J. Thomas, Introduction to Surface Chemistry and Catalysis, Wiley: New York (1994).

2.R.A. van Santen and J.W. Niemantsverdriet, Chemical Kinetics and Catalysis, Plenum: New York (1995).

3.M. Temkin, Acta Physicochim. URSS 13 (1940) 1.

4.Catalysis from A to Z: a Concise Encyclopedia, (B. Cornits, W.A. Hermann, R. Schlogl¨ and C.-H. Wong, eds.). Wiley-VCH: Weinheim (2000).

5.M. Boudart in; Handbook of Heterogeneous Catalysis, Vol. 3 (G.Ertl. H. Knozinger¨ and J. Weitkamp, eds.), Wiley-VCH: Weinheim (1997), p. 958.

6.B.H. Davis in: Handbook of Heterogeneous Catalysis, Vol. 1 (G.Ertl. H. Knozinger¨ and J. Weitkamp, eds.), Wiley-VCH: Weinheim (1997), p. 13.

7.J. Trofast, Chem. Britain (1990) 432.

8.G.C. Bond, Heterogenous Catalysis: Principles and Applications, 2nd Edn., Oxford U.P: Oxford (1987).

9.J.J. Berzelius, Anals Chim. Phys. 61 (1836) 146.

10.A.J.B. Robertson, Platinum Metals Rev. 19 (1975) 64.

11.D. McDonald and L.B. Hunt, A History of Platinum, Johnson Matthey: London (1982).

12.G.C. Bond, Catalysis by Metals, Academic Press: London (1962).

13.V. Ponec and G.C. Bond, Catalysis by Metals and Alloys, Elsevier: Amsterdam (1995).

14.R.J. Farrauto and C.H. Bartholomew, Fundamentals of Industrial Catalytic Processes, Chapman and Hall: London (1997).

15.C.N. Satterfield, Hetreogeneons Catalysis in Practice, 2nd . Edn., McGraw-Hill: New York (1991).

16.J.A. Dumesic, D.F. Ruda, L.M. Aparicio, J.E. Rekoske and A.A. Trevino, The Microkinetics of Heterogeneous Catalysis, Am. Chem. Soc.: Washington DC (1993).

17.R.J. Wijngaarden, A. Kronberg and K.R. Westerterp, Industrial Catalysis, Wiley-VCH: Weinheim (1998).

18.J.W.E. Coenen in: Perspectives in Catalysis, (R. Larsson, Ed.), C.W.K. Gleerup: Lund (1981), p. 19.

19.G.C. Bond, Chem. Soc. Rev. 20 (1991) 441.

20.IUPAC Manual of Symbols and Terminology for Physicochemical Qunatities and Units, App. II— Part II, Heterogeneons Catalysis, (R.C. Burwell Jr., ed), Pure and Appl. Chem. 14 (1976) 71.

21.M. Boudart, Chem. Rev. 95 (1995) 661.

22.M. Boudart and G. Djega-Mariadassou, Kinetics of Heterogeneous Catalytic Reactions, Princeton Univ. Press: New York (1984).

23.F.H. Ribeiro, A.E. Schach von Wittenau, C.H. Bartholomew and G.A. Somorjai, Catal. Rev.- Sci. Eng. 39 (1997) 49.

24.C.O. Bennett and M. Che, J. Catal. 120 (1989) 293.

25.H.S. Taylor, Chem. Rev. 9 (1931) 1.

26.C.N. Hinshelwood, Kinetics of Chemical Change, Clarendon Press: Oxford (1940).

27.Contact Catalysis (Z.G. Szabo´ and D. Kallo,´ eds.) Elsevier: Amsterdam (1976): vol. 1, #2.2.

28.O.A. Hougen and K.M. Watson, Chemical Process Principles, Wiley: New York (1948).

29.R.H. Yang and O.A. Hougen, Chem. Eng. Prog. 46 (1950) 146.

30.K.J. Laidler, Chemical Kinetics, Harper and Row: New York (1987).

31.G.C. Bond, R.H. Cunningham and J.C. Slaa, Topics Catal. 1 (1994) 19.

32.R.I. Masel and Wei Ti Lee, J. Catal. 165 (1997) 80.

33.G.C. Bond, A.D. Hooper, J.C. Slaa and A. O. Taylor, J. Catal. 163 (1996) 319.

34.G.A. Martin, Bull. Soc. Chim. Belg. 105 (1995) 131.

35.J.M. Hermann, Appl. Catal. A: Gen. 156 (1997) 285.

36.G.C. Bond, Ind. Eng. Chem. Res. 36 (1997) 3173; Catal. Today 17 (1993) 399.

37.V.P. Zhdanov and B. Kasemo, J. Catal. 170 (1997) 377.

38.V.P. Zhdanov and B. Kasemo, Surf. Sci. Rep. 39 (2000) 25.

39.P. Stolze, Prog. Surf. Sci. 65 (2000) 65.

40.S.B. Shang and C.N. Kenney, J. Catal. 134 (1992) 134.

41.W.L. Holstein and M. Boudart, J. Phys. Chem. B 101 (1997) 9991.

42.G.C. Bond and P.B. Wells, Adv. Catal. 15 (1964) 92.

43.R. Burch, Catal To-day 10 (1991) 233.

44.M. Che, C.O. Bennett, Adv. Catal. 36 (1989) 55.

45.R. Burch in Specialist Periodical Reports: Catalysis, Vol. 7 (G.C. Bond and G. Webb, eds.), Roy. Soc. Chem. (1985), p. 149.

46.Active Centres in Catalysis, (R. Burch, ed.), Catal. Today 10 (1991) 233.

47.G.A. Somorjai, Langmuir 7 (1991) 3176.

48.G.A. Somorjai, Adv. Catal. 26 (1977) 2.

49.H.S. Taylor, Proc. Roy. Soc. A 108 (1925) 105; J. Phys. Chem. 30 (1926) 145; 31 (1927) 277.

50.M. Boudart, Adv. Catal. 20 (1969) 153.

51.M. Boudart, A.W. Aldag, J.E. Benson, N.A. Dougharty and C.G. Harkins, J. Catal. 6 (1966) 92.

52.A.D. O Cinneide and J.K.A. Clarke, Catal. Rev. 7 (1972) 213.

53.G.C. Bond, J. Catal. 136 (1992) 631.

54.S.V. Norval, S.J. Thomson and G. Webb, Appl. Surf. Sci. 4 (1980) 51.

55.E.K. Rideal, Concepts in Catalysis, Academic Press: London (1968).

56.B.M.W. Trapnell, Adv. Catal. 3 (1951) 1.

57.A.N. Mal’tsev, Russ. J. Phys. Chem. 61 (1987) 1504.

58.G.A. Martin, Catal. Rev. - Sci. Eng. 30 (1988) 519.

59.A. Frennet, Catal. Rev. 10 (1974–5) 37.

60.A. Frennet, Catal. Today 12 (1992) 131.

61.C.T. Campbell, Ann. Rev. Phys. Chem. 41 (1990) 775.

62.D. Farin and D. Avnir, J. Am. Chem. Soc. 110 (1988) 2039; J. Catal. 120 (1989) 55.

63.J.J. Carberry J. Catal. 114 (1988) 277.

64.R. van Hardeveld and F. Hartog, Adv. Catal. 22 (1972) 75.

65.R. van Hardeveld and F. Hartog, Surf. Sci. 17 (1969) 90.

66.R. van Hardeveld and F. Hartog, Surf. Sci. 15 (1969) 189.

67.L.P. Ford, P. Blowers and R. I. Masel, J. Vac. Sci. Technol. A 17 (1999) 1705.

68.J. R. Anderson, Sci. Prog., Oxford. 69 (1985) 461.

69.J.R. Anderson, Structure of Metallic Catalysts, Academic Press: New York (1975).

70.E.G. Schlosser, Ber. Bunsenges. Phys. Chem. 73 (1969) 358.

71.G.C. Bond and R. Burch in: Specialist Periodical Reports: Catalysis, Vol. 6 (G.C. Bond and G. Webb, eds.), Roy. Soc. Chem. (1983), p. 27.

72.B.J. Kip, F.B.M. Duivenvoorden, D.C. Koningsberger and R. Prins, J. Catal. 106 (1986) 26; J. Am. Chem. Soc. 108 (1986) 5633.

73.I. Alstrop and N.T. Anderson, J. Catal. 104 (1987) 466.

74.W.R. Patterson and J.J. Rooney, Catal. Today. 12 (1992) 113.

75.Z. Schay and P. T´et´enyi, J. Chem. Soc. Faraday Trans. I 75 (1979) 1001.

76.R.W. Joyner and E.S. Shpiro, Catal. Lett. 9 (1991) 239.

77.J.H. Sinfelt, Catal. Rev. - Sci. Eng. 9 (1974) 147.

78.J.H. Sinfelt in: Catalysis—Science and Technology’ (J.R. Anderson and M. Boudart, eds.) Springer-Verlag, Berlin: (1981). p. 257.

79.J.H. Sinfelt and J.A. Cusumano, Adv. Mater. Catal. (1977) 1.

80.J.H. Sinfelt, Acc. Chem. Res. 20 (1987) 134.

81.J.H. Sinfelt, Internat. Rev. Phys. Chem. 7 (1988) 281.

82.J.K.A. Clarke, Chem. Rev. 75 (1975) 291.

83.J.K. Strohl and T.S. King, J. Catayl. 116 (1989) 540; 118 (1989) 53.

84.W. Linert and R.F. Jameson, Chem. Soc. Rev. 18 (1989) 477.

85.G.C. Bond, Appl. Catal. A: Gen.191 (2000) 23.

86.A.K. Galwey, Thermochim. Acta 294 (1997) 205; Adv. Catal. 26 (1977) 247.

87.J.J. Rooney. J. Molec. Catal. A: Chem. 96 (1995) L1.

88.A.K. Galwey, J. Catal. 84 (1983) 270.

89.G. C. Bond, M.A. Keane, H. Kral and J.A. Lercher, Chem. Rev. - Sci. Eng. 42 (2000) 323.

90.G.M. Schwab, Adv. Catal. 2 (1950) 251.

91.W.C. Conner and W. Linert, Orient. J. Chem. 5 (1989) 204.

92.K. H´eberger, S. Kem´eny and T. Vidoczy,´ Internat. J. Chem. Kin. 19 (1987) 171.

93.Z. Karpinski´ and R. Larsson, J. Catal. 168 (1997) 532.

94.G.C. Bond, Z. Phys. Chem. NF 144 (1985) 21.

95.G.C. Bond and R. H. Cunningham, J. Catal. 166 (1997) 172.

96.W.C. Conner Jr., J. Catal. 78 (1982) 238.

97.W.C. Conner Jr. and W. Linert, Orient. J. Chem. 5 (1989) 304.

98.L.K. Doraiswamy and D.G. Tajbl, Catal. Rev. 10 (1974–5) 177.

99.J.J. Carberry, Catal. Rev. 3 (1970) 61.

100.G.C. Bond and Xu Lin, J. Catal. 169 (1997) 76.

101.G.C. Bond and A.D. Hooper, React. Kinet. Catal. Lett. 68 (1999) 5; A.D. Hooper, PhD thesis, Brunel University, (2000).

102.C. O. Bennett, Adv. Catal. 44 (1999) 330.

103.H. Kobayashi and M. Kobayashi, Catal. Rev. 10 (1974–5) 139.

104.P. Biloen, J. Molec. Catal. 21 (1983) 17.

105.A. Frennet and C. Hubert, J. Molec. Catal. A: Chem. 163 (2000) 163.

106.C.O. Bennett, Am. Chem. Soc. Symp. Ser. 178 (1982) 1.

107.C.T. Campbell, Adv. Catal. 36 (1989) 2.

108.J. Sheridan, J. Chem. Soc. (1945), 133, 301.

109.G.C. Bond and J. Sheridan, Trans. Faraday Soc. 48 (1952) 651.

110.G.C. Bond, J. Chem. Soc. (1958) 2705.

111.G.C. Bond and R. S. Mann, J. Chem. Soc. (1958) 4738.

112.K.C. Campbell and S.J. Thomson, Prog. Surf. Membrane Sci. 9 (1975) 163.

113.R.L. Burwell Jr., Langmuir 2 (1986) 2.

114.F.G. Gault, Adv. Catal. 30 (1981) 1.

115.R.L. Burwell Jr., Catal. Rev. 7 (1972–3) 25.

116.C. Kemball, Biograph. Mem. Fellows Roy. Soc. 21 (1975) 517 (H.S. Taylor).

117.M. Polanyi and J. Horiuti, Trans. Faraday Soc. 30 (1934) 1164.

118.A. Farkas, L. Farkas and E.K. Rideal, Proc. Roy. Soc. A 146 (1934) 630.

119.G.C. Bond, J. Sheridan and D.H. Whiffen, Trans. Faraday Soc. 48 (1952) 715.

120.G.C. Bond, J. Chem. Soc. (1958) 4288.

121.K. Morikawa, W. A. Benedict and H.S. Taylor, J. Am. Chem. Soc. 57 (1935) 592; 58 (1936) 1795.

122.G.C. Bond, Trans. Faraday Soc. 52 (1956) 1235.

123.G.C. Bond and J. Turkevich, Trans. Faraday Soc. 49 (1953) 281.

124.G.C. Bond, J.J. Phillipson, P.B. Wells and J.M. Winterbottom, Trans. Faraday Soc. 60 (1964) 1847.

125.R.L. Burwell Jr., Catal. Rev. 7 (1973) 25.

126.A. Loaiza, M-D. Xu and F. Zaera, J. Catal. 159 (1996) 127.

127.L. Guczi and P. T´et´enyi, Acta Chim. Acad. Sci.71 (1972) 341.

128.L. Guizi, A. S´ark´any and P. T´et´enyi, Z . Phys. Chem. NF 74 (1971) 26.

129.L. Guczi, K.M. Sharan and P.T´et´enyi, Monatshefte Chem. 102 (1971) 187.

130.L. Guczi, and P. T´et´enyi, Z. Phys. Chem. 237 (1968) 356.

131.Z. Pa´al and S.J. Thompson, J. Catal. 30 (1973) 96.

132.G.F. Berndt in Specialist Periodical Reports: Catalysis, Vol. 6 (G.C. Bond and G. Webb, eds.),

Roy. Soc. Chem. (1983), p. 144.

133.F. Gault, V. Amir-Ebrahimi, F. Gavin, P. Parayre and F. Weisang, Bull. Soc. Chim. Belg. 88 (1979) 475.

134.H.C. de Jongste and V. Ponec, Bull. Soc. Chim. Belg. 88 (1979) 453.

135.H. Charcosset, Internat. Chem. Eng. 23 (1983) 187, 411.

136.J.H. Sinfelt, J. Phys. Chem. 90 (1986) 4711.

137.R. Burch, Acc. Chem. Res. 15 (1982) 24.

138.V. Ponec, J. Molec. Catal. A: Chem. 133 (1998) 221.

139.E.G. Allison and G.C. Bond, Catal. Rev. 7 (1973) 233.

140.R.L. Moss in: Specialist Periodical Reports: Catalysts, Vol. 1 (C. Kemball and D.A. Dowden, eds.), Roy. Soc. Chem. (1977), p. 37; Vol. 4 (C. Kemball and D.A. Dowden, eds.), Roy. Soc. Chem. (1981), p. 31.

141.D.A. Dowden in: Specialist Periodical Reports: Catalysis, Vol. 2 (C. Kemball and D.A. Dowden, eds.), Roy. Soc. Chem. (1978) p. 1.

142.L. Guczi and A. S´ark´any: in Specialist Periodical Reports: Catalysis, Vol. 11 (J.J. Spivey and S.K. Agarwal, eds.), Roy. Soc. Chem. (1994), p. 318.

143.V. Ponec, Appl. Catal. A: 222 (2001) 31.

144.K.A. Fichthorn and W.H. Weinberg, Langmuir 7 (1991) 2539.

145.R. Larsson, Z. Phys. Chem. Leipzig 268 (1987) 721.

146.R. Larsson, Catal. Lett. 11 (1991) 137; 16 (1992) 273.

147.R. Larsson, J. Molec. Catal. 55 (1989) 70.

FURTHER READING

Bimetallic catalysis 61, 78–82, 135–143

Compensation phenomena 67, 87, 90, 95, 98, 144–146