Catalyst Deactivation in Diborane Decomposition
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Catalysis Letters Vol. 105, Nos. 3–4, December 2005 ( 2005) DOI: 10.1007/s10562-005-8690-9
Catalyst deactivation in diborane decomposition Mats So¨derlunda, Pa¨ivi Ma¨ki-Arvelaa, Kari Era¨nena, Tapio Salmia, Risto Rahkolab, and Dmitry Yu. Murzina,* a
Laboratory of Industrial Chemistry, Process Chemistry Centre, A˚bo Akademi University, Biskopsgatan 8, 20500 Turku, Finland b Finnish Chemicals, A¨etsa¨, Finland
Received 18 May 2005; accepted 17 August 2005
Both thermal and catalytic decomposition of diborane resulting in borane as the main product were investigated under the pressure and temperature ranges of 2–15 bar and 100–300 C, respectively over Al2O3 and Pt/Al2O3 in a fixed bed reactor. Catalytic decomposition rate was essentially higher than the thermal decomposition, however the catalyst deactivation was substantial. KEY WORDS: diborane; catalytic decomposition; deactivation; boron hydrides.
1. Introduction Diborane (B2H6) is a relatively stable, commercially available substance, being a gas at room temperature with the boiling point of )92.6 C. Diborane is a toxic compound exhibiting a LD50 value in humans 30– 90 mg/m3 for 4 h of exposure [1]. It is highly reactive with water and oxygen giving in the presence of water almost instantaneously boric acid: B2 H6 þ 6H2 O ! 2B(OH)3 þ 6H2
ð1Þ
Diborane is an important product used as a selective reducing agent in organic chemistry. It can be produced for instance via contacting boron trifluoride with sodium borohydride in diethyl glycol dimethyl ether [2]. 3NaBH4 þ 4BF3 diglyme2B2 H6 þ 3NaBF4
ð2Þ
Two other routes, where diborane is formed as a product, are the reactions between sulphuric acid and sodium borohydride or sodium borohydride and iodine: 2NaBH4 þ H2 SO4
B2 H6 þ 2H2 þ Na2 SO4
2NaBH4 þ I2 diglymeB2 H6 þ 2NaI þ H2
ð3Þ ð4Þ
Diborane can decompose to pentaborane (B5H11), decaborane (B10H14) as well as to small amounts of tetraborane (B4H10). After 3 months storage about 8% of diborane was decomposed under 1 bar pressure [3]. In the thermal decomposition of diborane and tetraborane, pentaborane (B5H11) can be formed [3]. Tetraborane can be slowly formed from the decomposition of diborane as follows [4]: 2B2 H6 ! B4 H10 þ H2
* To whom correspondence should be addressed. E-mail: dmurzin@abo.fi
ð5Þ
and it is unstable at room temperature and at higher temperatures, i.e. it can decompose to B4H8 and B3H7 [5]. Pentaborane is additionally formed in the thermal decomposition of diborane at 250 C and 0.16 bar with the yield of 33% [3]: 5B2 H6 ! 2B5 H9 þ 6H2
ð6Þ
In the pyrolysis of diborane decaborane (B10H14) could be formed at temperatures up to 240 C [2]. As apparently clear from the short consideration presented above the boron chemistry is very complex. The industrial use of diborane can be thus limited due to its instability and reactivity. The catalytic decomposition of diborane over several catalysts was reported in the literature. Ni, Fe2O3, Cr2O3 [6], Ni(100) [7], Ru(0001) [8], silica gels [9,10], silica alumina surfaces [10], Ni/Al2O3, Pt [1
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