Rh3+ and Rh3+-diamine complexes intercalated in γ-titanium hydrogen phosphate.: Synthesis, characterisation and catalytic activity towards aniline oxidative carbonylation processes

New materials containing Rh(III) ions or Rh(III)-diamine complexes [(L = 2,2'-bipyridyl (bipy); 1,10-phenanthroline (phen); 2,9-dimethyl-1,10-phenanthroline (dmp)] intercalated in gamma-titanium phosphate (gamma-TiP) are described. The compounds have formula gamma-TiPHxRhy. tH(2)O (x= 2-3y; 0 <y <0.18; 1.5 <t<2.2), hereafter indicated as gamma-TiPRh, and gamma-TiPHxRhyLz. nH(2)O (x = 2-3y; 0 < y < 0.25; 0 < z < 0.35; 2.5 < n < 4.2), hereafter indicated as gamma-TiPRhL. They were prepared by contacting samples of gamma-TiP and gamma-TiPL with appropriate volumes of Rh(III) solution, at 45 degrees C. The materials were characterised by X-ray diffraction pattern and TG-DTA techniques. Their catalytic activity towards aniline carbonylation was tested. The compounds catalyse the oxidative carbonylation of aniline to diphenylurea (DPU) and/or methylphenylcarbamate (MPC). When the reaction is carried out in methanol or CH3CN, at 70-90 degrees C under moderate pressure of a CO/O-2 mixture (P-tot = 0.5 divided by 5 MPa; P(O-2)= 0.1 divided by 0.8 MPa),;aniline is converted to DPU with a yield of 90% with respect to CO. The catalysts recovered and reused do not show any decrease of activity. When more drastic temperature conditions (110-150 degrees C) are used, the carbonylation is not selective and the yield off carbon monoxide fixation is strongly dependent on the solvent. In CH3CN, aniline is converted into DPU with a selectivity of 90% and the yield of CO fixation is still high (85%). Conversely, in methanol, N-phenylmethylcarbamate (MPC) is the main product with relevant amounts of CO2 formed and a CO fixation yield not higher than 70%. Under these conditions, the catalysts when reused have shown a decrease of activity. On the basis of XPS analysis, it has been ascertained that the decrease in activity is due to an irreversible reduction of Rh3+ to Rh-o that causes the release of the metal from the support and the consequent deactivation of the catalyst. (C) 2000 Elsevier Science B.V. All rights reserved.