Aerosol-Derived Bimetallic Alloy Powders: Bridging the Gap

Abstract

We present aerosol-derived alloy powders as a uniquely useful platform for studying the contribution of the metal phase to multifunctional supported catalysts. Multimetallic heterogeneous catalysts made by traditional methods are usually nonhomogenous while UHV-based methods, such as mass selected clusters or metal vapor deposited on single crystals, lead to considerably more homogeneous, well-defined samples. However, these well-defined samples have low surface areas and do not lend themselves to catalytic activity tests in flow reactors under industrially relevant conditions. Bimetallic alloy powders derived by aerosol synthesis are homogeneous and single phase and can have surface areas ranging 1-10 m2/g, making them suitable for use in conventional flow reactors. The utility of aerosol-derived alloy powders as model catalysts is illustrated through the synthesis of single phase PdZn which was used to derive the specific reactivity of the L10 tetragonal alloy phase for methanol steam reforming. Turnover frequencies on unsupported PdZn were determined from the experimentally determined metal surface area to be 0.21 molecules of methanol reacted per surface Pd at 250 °C and 0.06 molecules of CO oxidized to CO2 per surface Pd at 185 °C. The experimentally measured activation energies for MSR and CO-oxidation on PdZn are 48 and 87 kJ/mol, respectively

CuO/ZnO catalysts for methanol steam reforming: The role of the support polarity ratio and surface area

“…In line with this finding, a recent study about the influence of ZnO facets on the performances of Pd/ZnO catalysts for MSR also reached the same conclusion [41,42]. Authors reported that at comparable Pd/ZnO catalyst composition, the polar sample was more selective than the nonpolar one due to the preferential formation of the PdZnl3 phase, which is selective toward CO2, on the polar ZnO [41,42]. From the results compiled in Tables 1 and 3, it can be inferred that the polarity ratio of ZnO support does not exert any promoting effect on activity but clearly affects the selectivity (Fig.…”

“…ZnO was also found to affect the activity and selectivity of PdZnO catalysts in MSR reaction [32]. In line with this finding, a recent study about the influence of ZnO facets on the performances of Pd/ZnO catalysts for MSR also reached the same conclusion [41,42]. Authors reported that at comparable Pd/ZnO catalyst composition, the polar sample was more selective than the nonpolar one due to the preferential formation of the PdZnl3 phase, which is selective toward CO2, on the polar ZnO [41,42].…”

Strong metal-support interaction and alloying in Pd/ZnO catalysts for CO oxidation

“…This reversibility was confirmed by their Zn LMM Auger measurements by a shoulder at higher E kin in the reduced state, representing the intermetallic compound. More recent measurements confirmed the alloying process in aerosol-derived PdZn particles [16] (335 eV → 335.7 eV) and by monitoring the Zn3d peak [17]. A difference from metallic palladium (335 eV) to monolayer PdZn (335.3 eV) and multilayer PdZn (335.8 eV) has been reported by Rameshan et al [18].…”

Hydrogen production by methanol steam reforming: Catalytic performance of supported-Pd on zinc–cerium oxides’ nanocomposites

“…In particular, the presence of well-dispersed ZnO domains on the support surface and/or as patches onto the PdZn bimetallic crystallites under MSR reaction condition, seems to be crucial for obtaining high turnover frequencies. Nonetheless, other authors have concluded that just the right PdZn alloy (namely, tetragonal PdZn␤ 1 ) suffices to grant high S CO2 and high TOF values [26], albeit under MSR conditions oxidized Zn species seem to be present in their pre-reduced bimetallic particles as was suggested by Lorenz et al [28] based on their relevant XPS spectra, probably because those alloy powders were again exposed to water.…”

“…This pretreatment was chosen to ensure the formation of a PdZn alloy (wherever applicable [7,[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]) prior to evaluating the catalysts' performance. The MSR study was done using 'temperature steps', from 398 to 623 K (1 h/ea.…”