Improved CO Oxidation Activity in the Presence and Absence of Hydrogen over Cluster-Derived PtFe/SiO₂ Catalysts

Abstract

The catalytic performance of cluster-derived PtFe/SiO(2) bimetallic catalysts for the oxidation of CO has been examined in the absence and presence of H(2) (PROX) and compared to that of Pt/SiO(2). PtFe(2)/SiO(2) and Pt(5)Fe(2)/SiO(2) samples were prepared from PtFe(2)(COD)(CO)(8) and Pt(5)Fe(2)(COD)(2)(CO)(12) organometallic cluster precursors, respectively. FTIR data indicate that both clusters can be deposited intact on the SiO(2) support. The clusters remained weakly bonded to the SiO(2) surface and could be extracted with CH(2)Cl(2) without any significant changes in their structure. Subsequent heating in H(2) led to complete decarbonylation of the supported clusters at approximately 350 degrees C and the formation of Pt-Fe nanoparticles with sizes in the 1-2 nm range, as indicated by HRTEM imaging. A few larger nanoparticles enriched in Pt were also observed, indicating that a small fraction of the deposited clusters were segregated to the individual components following the hydrogen treatment. A higher degree of metal dispersion and more homogeneous mixing of the two metals were observed during HRTEM/XEDS analysis with the cluster-derived samples, as compared to a PtFe/SiO(2) catalyst prepared through a conventional impregnation route. Furthermore, the cluster-derived PtFe(2)/SiO(2) and Pt(5)Fe(2)/SiO(2) samples were more active than Pt/SiO(2) and the conventionally prepared PtFe/SiO(2) sample for the oxidation of CO in air. However, substantial deactivation was also observed, indicating that the properties of the Pt-Fe bimetallic sites in the cluster-derived samples were altered by exposure to the reactants. The Pt(5)Fe(2)/SiO(2) sample was also more active than Pt/SiO(2) for PROX with a selectivity of approximately 92% at 50 degrees C. In this case, the deactivation with time on stream was substantially slower, indicating that the highly reducing environment under the PROX conditions helps maintain the properties of the active Pt-Fe bimetallic sites.

Green catalysis for selective CO oxidation in hydrogen for fuel cell

“…Combing the catalytic performances and the IR results, we propose that the surface OH on FSM-16 is highly reactive 50 toward CO adsorbed on Pt nanoparticles at the interface of Pt and FSM-16. As depicted in Fig.…”

“…The application of mesoporous silica in PROX opens a new potential way for the resolution. The most valuable and 50 interesting finding is that the surface silanols in mesoporous silica can play as the "oxidant" to initiate the CO reaction. This may release the confliction in the modification for the adsorption between CO and Pt, in which too much weakened adsorption will accelerate the side oxidation of H 2 .…”

“…Furthermore, in the adsorption of 13 CO or a mixture of 12 CO and 13 CO, gaseous 13 CO 2 peak was also observed at 2280 cm -1 . As a strong comparison, none of CO 2 peak was observed in the CO adsorption over the inactive 50 Pt(p)/HMM-1 or Pt/SiO 2 catalyst. It should be noted that no oxygen source was presented except the FSM-16 support in the adsorption of 12 CO or 13 CO.…”

“…The effect of zeolites architecture was also investigated, and difference among various zeolites was observed as following: Pt/A>Pt/mordenite>Pt/X. Moreover, dependence of oxidation activity on the pore 50 diameter of A zeolite was also observed. The higher catalytic performance of Pt/3A was attributed to the "shape selectivity" by the dimension of 3 Ǻ pore diameter, which may inhibit the admission of CO 2 molecule and suppress the reverse watergas-shift side reaction.…”

“…3,23 Further efforts have been made to 55 prepare bimetallic systems with uniform composition between Pt and promoters, which can improve the cooperative effects between CO adsorption and O 2 activation sites. 50,51 By using organometallic precursors (Pt 5 Fe 2 (1,5-cyclooctadiene)(CO) 12 or PtFe 2 (1,5-cyclooctadiene)(CO) 8 ), the cluster-derived 1 wt% 60 PtFe/SiO 2 catalysts show a relatively uniform Fe:Pt composition and particle-size distribution, which result in higher activity and selectivity than the 1 wt% Fe-Pt/SiO 2 catalyst prepared by the incipient wetness impregnation method. the CO conversion was improved in the presence of H 2 at the low temperature range (<353 K), it decreased with further higher reaction temperature and far from the complete CO reduction.…”