EFFECT OF OH GROUPS ON PH3 DECOMPOSITION ON A MOO3 AL2O3 CATALYST/

The adsorption and decomposition of phosphine have been studied on MoO 3/Al2O3 and on the OH-depleted catalyst MoO3/(CH3)3Si-O-Al2O3, using t ransmission IR spectroscopy and mass spectroscopy at 300-800 K. On MoO 3/Al2O3, some PD3 adsorbs dissociatively at 300 K, producing PD3-x and D atoms. The D atoms spill over onto the Al2O3 support, where they is otopically exchange with the Al-OH groups. Above 573 K, PH3 decomposes oxidatively on MoO3/Al2O3 producing H-2 (m/e = 2) gas and surface spe cies containing the H-P=O moiety. The MoO/(CH3)3Si-O-Al2O3 catalyst di ssociates some PH3 into PH3-x and H atoms at 300 K as well. The H atom s spill over onto the support, where they bind to the exposed oxygen a toms, producing H-bonded OH groups. At temperatures >573 K, PH3 also d ecomposes into H-2 gas on the silylated catalyst. However, because of the depletion of isolated OH groups by silylation, H-P=O(a) is not pro duced in this case. The results indicate that isolated Al-OH groups ar e essential as oxidizing agents for the oxidative decomposition of PH3 into H-P=O species on MoO3/Al2O3. The removal of the protons of the i solated Al-OH groups by silylation with (CH3)3SiCl at 473 K is effecti ve in blocking the pathway to the formation of the H-P=O moiety.