Bimetallic clusters in zeolites

A number of bimetallic carbonyl clusters such as Rh6 xIrx(CO)i6/NaY (x= 1-4),[ii.i5] [Fe2Rh4(CO)is]2-/NaY 3 and HRuCo3(CO)i2/NaYt ] have also been similarly synthesized by the ship-in-a-bottle technique and characterized by IR, EXAFS, UV and Raman spectroscopy, and are listed in Table 2. 

Co-0 bonds from the Si or A1 oxide surface. The RuCu bimetallic nanoparticle 

6 Nanowires in mesoporous channels and their unique properties 

FSM-16, which may be due to the dominant interaction of nanowires with the inner acidic surface of the FSM-16 pores. The adsorption of hydrogen for Pt nanowires was one or two-orders of magnitude smaller than that for nanoparticles. In the IR carbonyl adsorption spectrum, Pt nanowires gave a weak band at 2080 cm corresponding to journal carbonyls, which was shifted to higher frequency than in the Pt nanoparticles (2060 cm ). This shift may reflect the electron-deficiency of the Pt atoms or the dipole coupling of CO on Pt nanowires in mesopores.  

By varying the exposure time to UV-light, it is found by TEM and XAFS that the Pt nanoparticles are initially formed by the photo-reduction of the impregnated Pt cations in the mesopores. Subsequently, [PtClg] - ions migrate in the vicinity of the nanoparticles and are reduced on the surface and extend into the nanowires in the confined channels of FSM-16, as represented in Fig. 10(a). Ryoo reported the thermal preparation of the Pt nanowires in MCM-41 by the stepwise H2-reduction of Pt ions that were added to the pre-reduced Pt/MCM-41 above 823 As catalytic test reactions for Pt nanowires/FSM-16, Ichikawa et al. studied 

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Ship-in-a-Bottle Synthesis of Bimetallic Clusters in Zeolites... 

M6riaudeau et al. have prepared platinum-tin [238] and platinum-indium [239] bimetallic clusters in Y zeolite which were characterized using H2 and CO chemisorption, TEM and STEM-EDX analysis, IR and XPS spectroscopies. Pla-... 

The same workers (234) also studied the methanation behavior of bimetallic clusters of Ru/Ni and Ru/Cu in zeolite Y. Such clusters can be formed by metals, such as ruthenium and copper which are immiscible as bulk metals (235, 236). The turnover numbers versus bimetallic cluster composition are shown in Fig. 22. Dilution of ruthenium with copper clearly causes a marked decrease in specific activity. This decrease in activity is also accompanied by a decrease in methanation selectivity. This was attributed to an inhibiting effect of copper on the ruthenium hydrogenolysis activity. 

A detailed study of iron-promoted rhodium clusters was conducted by Schii-nemann et al. [235] using TPR, FTIR, TEM and Mossbauer spectroscopy. NaY was exchanged with Fe ions in FeS04 solutions, then rhodium was exchanged from [Rh(NH3)5Cl]Cl2 solutions. The co-exchanged zeolite was calcined from room temperature to 500 °C with a ramp of 0.5 °C min. After reduction at 500°C most of the iron remained in ionic form, but bimetallic clusters with a low Fe content were also formed. Treatment in NaOH of the reduced zeolite followed by calcination and reduction maximized the Fe content that attained ca. 50% according to ferromagnetic resonance data. The Rh-Fe clusters were disrupted in a CO atmosphere with formation of rhodium and iron carbonyls. 

A series of Pt-Ni bimetallic clusters with varying Ni/Pt ratios were prepared and characterized by Larsen and Haller [253]. KL zeolite was co-impregnated with Ni(N03)2 and Pt(NH3)4(N03)2, calcined at 723 K and reduced at 773 K. From EXAFS, X-ray absorption near edge structure (XANES) and chemisorption measurements it was concluded that bimetallic particles were formed with a Pt-rich core and a Ni-rich surface and there was an electron transfer from Ni to Pt atoms in the clusters. 

Li and Armor reported that Co-exchanged zeolites present a very high catalytic performance for the CH4-SCR, even in oxygen excess conditions [1, 3], Bimetallic Pt-and Pd-Co zeolites have revealed an increase of activity, selectivity towards N2 and stability, when compared with monometallic Co catalysts [4-8] even in the presence of water in the feed. Recent works show that these catalytic improvements are due to the presence of specific metal species as isolated metal ions, clusters and oxides and their location inside the cavities or in the external surface of zeolite crystallites [9, 10],... 

In the preparation of faujasite zeolite-supported Pt-Re catalysts, bimetallic PtRe clusters have been reported to be predominantly formed when a carbonyl rhenium precursor (Re2(CO)io) is contacted with zeolite in which platinum has been previously introduced and reduced. The preexisting Pt clusters may act as nucleation sites. After reduction, these Pt-Re systems show a high selectivity to CH4 in the hydrogenolysis of n-heptane [58]. 

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