Preparation, characterization and catalytic hydroformylation properties ofcarbon nanotubes-supported Rh-phosphine catalyst

Two kinds of carbon nanotubes grown catalytically, as a novel material for catalyst carrier, were prepared and characterized. Propene hydroformylation catalyzed by the Rh-phosphine complex catalysts supported by carbon nanotu bes was investigated, and compared to that catalyzed by the Rh-phosphine co mplex catalysts supported by SiO2 (a silica gel), TDX-601 (a carbon molecul ar sieve), AC (an active carbon), and GDX-102 (a polymer carrier). Activity assay of the catalysts showed that the carbon nanotubes-supported Rh-phosp hine complex catalysts displayed not only high activity of propene conversi on but also excellent regioselectivity to the product butylaldehyde. Under the reaction conditions of 393 K, 1.0 MPa, C3H6/CO/H-2 = 1/1/1 (v/v), GHSV = 9000 ml (STP) h(-1) (g catal.)(-1), P/Rh = 9-12 (molar ratio), and Rh-loa ding at 0.1 mmol Rh(g carrier)(-1), the molar ratio of normal/branched (n/i ) aldehydes reached 12-13 at a turnover frequency (TOF) of 0.12 s(-1), corr esponding to propene conversion of similar to 32%. The characterization by using TEM, HRTEM, XRD, Raman, XPS, BET and temperature programmed desorptio n (TPD) methods indicated that the carbon nanofibers prepared were quite ev en nanotubes with the outer diameters at 15-20 nm and the inner diameters ( i.e., pore diameters) at similar to 3 nm. Each tube wall was constructed of many layers of carbon with graphite-like platelets in a cross-section orie ntation of 'parallel type' or 'fishbone type'; their C (1 s) electron bindi ng energy was about 0.5 eV lower than that of graphite. These results, toge ther with the results of comparative studies of the Rh-phosphine complex ca talysts supported by several other carriers, implied strongly that the tubu lar channels with the inner diameter of similar to 3 nm in the carbon nanos tructures and its hydrophobic surface consisting of six-membered C-rings pl ayed important roles in enhancing the activity of propene hydroformylation, especially the regioselectivity of butylaldehyde on the Rh-phosphine compl ex catalysts supported by them. (C) 1999 Elsevier Science B.V. All rights r eserved.