Hole-doped La1.85Sr0.15CuO4-delta X sigma (X = F, Cl) and electron-doped Nd1.85Ce0.15Cu4-delta X sigma halo-oxide catalysts for the selective oxidation of ethane to ethene

The catalytic performance and characterization of Ln(1.85)A(0.15) CuO4-delt a and Ln(1.85)A(0.15)CuO(4-delta)X(sigma) (Ln = La, Nd; A = Sr, Ce; X = F, Cl) for the oxidative dehydrogenation of ethane (ODE) to ethene have been i nvestigated. The hole-doped catalysts performed better than the electron-do ped ones. Under the reaction conditions of temperature, 660 degreesC; C2H6/ O-2/N-2 molar ratio, 2/1/3.7; and contact time, 1.67 x 10(-4) h g mL(-1); L a1.85Sr0.15CuO3.930Cl0.053 showed 82.8% C2H6 conversion, 73.2% C2H4 selecti vity, and 60.6% C2H4 yield; Nd1.85Ce0.15CuO3.981F0.092 showed 72.1% C2H6 co nversion, 61.8.0% C2H4 selectivity, and 44.6% C2H4 yield. The sustainable p erformance during a period of 60 h on-stream reaction at 660 degreesC demon strated that the F- and Cl-doped catalysts are durable. The results of X-ra y powder diffraction indicated that the Sr-substituted cuprates were of T s tructure whereas the Ce-doped cuprates were of T' structure. The results of X-ray photoelectron spectroscopic (XPS) studies revealed that there were C u2+ and Cu3+ in the Sr-doped cuprate catalysts and Cu+ and Cu2+ in the Ce-d oped cuprate catalysts. The results of the XPS, thermogravimetric analysis (TGA), and O-18(2)-pulsing studies demonstrated that the incorporation of h alide ions into the Ln(1.85)A(0.15)CuO(4-delta) lattice promoted the activi ty of lattice oxygen. By comparing the results of XPS, TGA,and Oz temperatu re-programmed desorption with the catalytic performance of the catalysts, w e conclude that (i) lattice O2- species at the surface are active for the s elective oxidation of ethane; (ii) in excessive amount, O- species accommod ated in oxygen vacancies are prone to induce the total oxidation of ethane; and (iii) a suitable Cu3+ or Cu+ concentration and/or oxygen nonstoichiome try in Ln(1.85)A(0.15)CuO(4-delta)X(sigma), are required for the best catal ytic performance of the catalysts. (C) 2001 Academic Press.