Journal of Catalysis 189, 195–208 (2000) A rticle ID jcat.1999.2695, available online at http://www.idealibrary.com on Effects of Oxidation–Reduction and Oxychlorination–Reduction Cycles on Pt–Ge/Al 2 O 3 Catalysts G eomar J. A rteaga, James A . A nderson, and Colin H . R ochester D epartm ent of Chem istry, D undee University, D undee DD 1 4H N, UK R eceived July 8, 1999; revised September 10, 1999; accepted September 28, 1999 Two Pt(0.3%)–Ge/Al 2 O 3 catalysts containing 0.15 and 0.45%Ge have been characterized by CO chemisorption and FTIR spectra of adsorbed CO after series of oxidation/reduction and oxychlori- nation/reduction cycles and have also been used for the catalytic hydroreforming of heptane. Catalysts after oxychlorination con- tained chloro- and oxychloro-Pt complexes which were responsible for the efficient spreading of Pt over the support surface and hence for the maintenance of a good Pt dispersion after reduction. XRD study of a more highly loaded catalyst gave no evidence for Pt–Ge alloy formation or for Ge 0 species. Reduced Cl-containing catalysts contained small clustered arrays of Pt atoms dispersed possibly as mats rather than particles over the GeO x -modified alumina such that all the exposed Pt atoms were influenced by an electron with- drawing effect of both Ge 2 + ions and Cl ions. Germanium did not block low-coordination Pt sites but may have partially decorated arrays of high coordination sites. Germanium partially stabilized Pt/Al 2 O 3 against loss ofactivity through coking. The dominant mutual effect of Ge and Cl in catalysts was a significant loss in hydrogenolysis selectivity, but gains in the selectivities of aromati- zation, isomerization, and cyclization reactions. The addition of Ge to Pt/Al 2 O 3 did not compromise the availability of Pt adsorption sites and only reduced by a small amount the turnover frequen- cies for heptane reforming reactions. Good activities were therefore maintained in the absence of Ge 0 or alloy formation during catalyst reduction. c ° 2000 Academic Press Key Words: Pt–Ge/Al 2 O 3 , CO adsorption on; Pt–Ge/Al 2 O 3 , hep- tane reforming over. INTRODUCTION The use of Pt–G e/A l 2 O 3 as a reforming catalyst at low pressure requires regular catalyst regeneration after sinter- ing and coking and therefore the behavior of Pt–G e/A l 2 O 3 after oxidation/reduction and oxychlorination/reduction treatments is of the utmost importance, but has received scant attention. The present study attempts to remedy this deficiency by studying the effects of repeated oxidation/ reduction cycles in the absenceof Cl (1, 2) and oxy- chlorination/reduction cycles (3) on catalytic behavior (as monitored by heptane reforming reactions) and surface properties (CO chemisorption, FTIR of adsorbed CO ). A catalyst containing high Pt and G e loadings was studied by XR D in order to assess the effects of treatment conditions on bulk catalyst structures. The reduction in hydrogen of Pt 4+ to Pt 0 in Pt–G e/A l 2 O 3 catalysts is complete below 673 K, but the oxidation state of the G e species after reduction depends on the method of catalyst preparation, metal loadings, and reduction con- ditions (4–7). Bouwman and Biloen (8) showed that G e 4+ and G e 2+ were present afterreduction at823 K,butaf- terreduction at923 K the catalyst contained G e 2+ with some G e 0 probably alloyed with Pt. A lloy phases Pt 2 G e, PtG e,and Pt 2 Ge 3 have been identified (9, 10).H owever, G oldwasser et al. (5) found no evidence for G e 0 in a cata- lyst which had been reduced at temperatures up to 973 K, although G e 0 in alloy and free G e particles have been re- ported after reduction at 1073 K (4, 7). Bimetallic Pt–G e, Pt 3 Ge 2 , and Pt 3 G e clusters have been reported for catalysts reduced at 673 K, although their formation was a function of catalyst preparation (6). A lloying ofPt and G e in Pt–G e/A l 2 O 3 catalysts can lead to significant losses in both dehydrogenation and hy- drogenolysisactivity (7).A ctivitiesfor benzene hydro- genation and butane hydrogenolysis were decreased by increasing G e loading, this being attributed to an elec- tronic effectof G e on Pt(5). H owever, for heptane re- forming isomerization activity was also decreased by in- creasing G e, but,in contrast, hydrogenolysis activity was increased (11). The activities of both reactions were en- hanced by the addition of H Cl during catalyst preparation (11), possibly because Cl partially inhibits alloy formation (4, 7). Catalytic behavior for octane reforming reactions was also dependent on the method ofcatalystprepara- tion (6). Coq et al. (12) have suggested from study of 2,2,3, 3-tetramethylbutane over Pt–G e/A l 2 O 3 thatthe addition of G e marginally favored a shift to central cleavage, indica ting that the properties of the surface Pt atoms were slight shifted toward those characteristic of larger Pt particles. EXPERIMENTAL Chlorine-free Pt/A l 2 O 3 catalystprecursors, designed to contain 0.3 and 3.0 wt% Pt after reduction, were prepared 195 0021-9517/00 $35.00 Copyrightc ° 2000 by A cademic Press A ll rights of reproduction in any form reserved.