584-Haack-ACAG-1992-103 - Applied Catalysis A General...

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Applied Catalysis A: General, 87 (1992) 103-114 Elsevier Science Publishers B.V., Amsterdam 103 APCAT A2296 Characterization of high-temperature calcined lanthanum-modified alumina by X-ray photoelectron spectroscopy and X-ray diffraction L.P. Haack, C.R. Peters, J.E. deVries and K. Otto Ford Motor Company, SRL Mail Drop S-3061, P.O. Box 2053, Dearborn, MI 48121-2053 (USA) (Received 3 February 1992, revised manuscript received 1 May 1992) Abstract Previous studies in this laboratory have shown that for the La/y-A&O,, system as the atomic ratio La/Al is increased from 0.05 to 2.0 the X-ray photoelectron spectroscopy (XPS) La 3d5/2 binding energy progressively decreases from 835.2 to 832.9 eV. The shifts in binding energy demonstrate a change in the coordination of lanthanum coinciding with a transformation from dispersed to particulate phases. It is of particular interest to understand more completely the chemical interaction between lanthana and alumina at lower lanthanum loadings, which is known to retard the sintering of y-alumina and promote catalysis. In this study lanthanum-modified alumina was calcined at high temperature ( 1500°C). Up to a La/Al ratio of 0.10, X-ray diffraction (XRD) identified the dominant lanthanum phase as lanthanum-P-alumina ( Laz03* 11 A&O,). The XPS La binding energy for lanthanum-/I-alumina was 835.2 eV, which corresponds to that measured previously for dispersed phase lanthanum in y-alumina. These results suggest that at La/Al<O.lO the highly dispersed La/y-A&O, species is a precursor of crystalline lanthanum-P-alumina formed at higher temperatures. At higher lanthanum concentrations XRD identified highly ordered crystalline LaAlO, and La,O,, consistent with the phase diagram of the La/Al,O, system. According to XPS binding energy shifts the precipitation of LaAlO, requires a higher lanthanum concentration at 925°C (y-alumina phase) than at 1500°C (/?-alumina phase). Keywords: catalyst characterization (XPS, XRD), catalyst preparation (impregnation), lanthanum/ alumina, lanthanum aluminate, lanthanum-~-alumina. INTRODUCTION Interest in lanthanum oxide as a catalyst promoter has been stimulated by observations of dramatic and unexpected catalytic behavior. The addition of lanthana has resulted in enhanced catalytic activities in the reduction of nitric oxide [ 1,2] and the hydrogenation of carbon monoxide [ 31. At low loading, lanthana inhibits the sintering of y-alumina [4-71 and acts to disperse sup- Correspondence to: L.P. Haack, Ford Motor Co., SRL Mail Drop S-3061, P.O. Box 2053, Dear- born, MI 48121-2053, USA. Tel. (+ 1-313) 5940043, fax ( + 1-313) 3237397.
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104 L.P. Haack et al./Appl. Catal. A 87(1992) 103-114 ported metals and enhance their activity [ 8-121. Since lanthana is an impor- tant component in modern automotive catalysts [ 131, the understanding of its interactions with y-alumina is of substantial importance in the continuing quest to improve emission control.
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584-Haack-ACAG-1992-103 - Applied Catalysis A General...

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