Synthesis and Characterization of Model MgO-Supported Catalysts with Pt−Mo Interactions

Abstract

MgO-supported platinum and platinum-molybdenum catalysts were prepared from organometallic precursors and characterized structurally to determine how the nature of the bimetallic precursors and the treatment conditions affected the interaction between the two metals. Samples were prepared from [PtCl 2 (PhCN) 2 ], [PtCl 2 (PhCN) 2 ] + [Mo(CO) 6 ], and {Pt[Mo(CO) 3 (C 5 H 5 )] 2 (PhCN) 2 } and characterized by infrared and extended X-ray absorption fine structure (EXAFS) spectroscopies, transmission electron microscopy, and chemisorption of H 2 , CO, and O 2 . The samples were treated in H 2 at 400°C prior to most of the characterizations. Incorporation of Mo reduced the chemisorption of CO and of H 2 . EXAFS spectra measured at the Pt L III edge and at the Mo K edge showed substantial Pt-Mo contributions with a Pt-Mo coordination number of about 2 and an average distance of 2.63 Å for the sample prepared from {Pt[Mo(CO) 3 (C 5 H 5 )] 2 (PhCN) 2 }. In contrast, no significant Pt-Mo contribution was observed for the sample prepared from [PtCl 2 (PhCN) 2 ] + [Mo(CO) 6 ]. Electron micrographs and EXAFS results show that interaction between Pt and Mo ions in the former sample helped to maintain the platinum in a highly dispersed form, with supported platinum clusters being smaller than about 10 Å.

Structure-Sensitivity of Propylene Hydrogenation over Cluster-Derived Bimetallic Pt-Au Catalysts

“…Chandler et al [22] have shown that in similar Pt 2 Au 4 cluster-derived catalysts, the amount of chemisorbed hydrogen is decreased in the presence of Au, and as a result, the Pt dispersion on these catalysts can be underestimated. Similar observations have also been reported for other bimetallic systems [23][24][25].…”

Synthesis and Structural Characterization of SiO2-Supported PtFe Catalysts Prepared from PtFe2(C8H12)(CO)8

“…Although a variety of mixed-metal organometallic cluster complexes are available [18], but because of the difficulties associated with handling of these compounds, stability issues of the bimetallic cluster cores, and poisoning effects due to the decomposition of the stabilizing ligands, only a small number have been used to date as precursors for the preparation of supported bimetallic catalysts. Examples of small supported bimetallic catalysts formed from organometallic cluster precursors with preformed metal-metal bonds have been reported for PtMo, PtW, PdMo, RuCu, RuSn, PdRu, ReIr, and PtRu combinations [9,[19][20][21][22][23][24][25][26][27][28][29][30][31], and have demonstrated the superiority of this approach for the preparation of new catalysts.…”

Supported Metal Cluster Catalysts

“…Bimetallic clusters on oxides have also been prepared from the following precursors: Pd 2 Mo 2 (CO) 6 (C 5 H 5 ) 2 − (PPh 3 ) 2 [17], PtMo 2 (CO) 6 (C 5 H 5 ) 2 (PhCN) 2 [19], PtW 2 − (CO) 6 (C 5 H 5 ) 2 (PhCN) 2 [20], Pt 2 − W 2 (CO) 6 (C 5 H 5 ) 2 (PPh 3 ) 2 [21], and [Ru 12 C 2 Cu 4 Cl 2 (CO) 32 ][PPN] 2 [22], among others cited elsewhere [15]. Platinum clusters incorporating as few as four atoms each, on average, are indicated by EXAFS data characterizing the Pt − W clusters [21].…”