Supporting Information
Direct Synthesis of Hydrogen Peroxide Over Au-Pd Catalysts Prepared by ElectrolessDeposition
Ana C. Alba-Rubio,†§ Anthony Plauck,†§ Eric E. Stangland,‡ Manos Mavrikakis,† and James A. Dumesic†,*
†Department of Chemical and Biological Engineering, University of Wisconsin-Madison. Madison, WI 53706, USA.
‡The Dow Chemical Company, Core R&D. Midland, MI 48674, USA.
* Corresponding author E-mail:
§ These authors contributed equally.
1 Synthesis of Au-Pd/SiO2 catalysts by electroless deposition (ED)
The Pd site density of the monometallic base catalyst (Pd/SiO2) was determined by CO chemisorption (using a surface stoichiometry of 2/3 for CO/Pd)(1) to calculate the amount of Au required for certain coverage. For example, the surface site density for the Pd/SiO2(ld) catalyst was 91 μmol Pd exposed/g catalyst by CO chemisorption, which means that 91 μmol Au/g catalyst should be deposited for a theoretical 1 monolayer (ML) Au coverage. The same bath was used for the preparation of all the bimetallic catalysts, and the amount of added Pd/SiO2 catalyst was adjusted to obtain the desired coverage. A large bath was prepared by adding 43.5 mg of precursor (KAu(CN)2) and 227 mg of N2H4·H2O to 240 mL of a NaOH solution with pH 9. That bath was divided into beakers (80 mL in each) and different amounts of Pd/SiO2 monometallic catalysts were added: 556 mg (for the theoretical 1MLAu-Pd/SiO2 catalyst), and 278 mg (for the theoretical 2MLAu-Pd/SiO2 catalyst). The third batch (no Pd/SiO2 added) was used to determine the stability with respect to formation of small Au particles(2).The UV-Visible adsorption spectrum of the ED bath was measured using a Beckman DU® 520 scanning spectrophotometer.A scan of water at pH 9.0 was used as the reference. The ED bath was stable for at least 3 h at room temperature under stirring (no adsorption bands appeared on the spectrum, not shown), longer than the time used for deposition of Au on Pd/SiO2.
2 Au-Pd/SiO2 catalysts: Characterization by FTIR
Table S1.FTIR peak positions and intensity ratios for Pd/SiO2 and Au-Pd/SiO2 catalysts.
Linear region (L) / Non-linear region (NL) / Linear/non-linear area (L/NL)L1 / L2 / L3 / L4 / NL1 / NL2 / NL3 / NL4
Pd/SiO2(hd) / 2113 / 2094 / 2065 / 2042 / 1971 / 1952 / 1890 / 1816 / 0.78
0.8MLAu-Pd/SiO2(hd) / 2076 / 2039 / 1939 / 1884 / 1826 / 0.46
Pd/SiO2(ld) / 2091 / 2066 / 1973 / 1939 / 1891 / 1833 / 0.12
0.69MLAu-Pd/SiO2(ld) / 2045 / 2013 / 1933 / 1868 / 0.16
Peak assignments referenced from(2),(3)
L1, L2: Pd0 terraces
L3, L4: low coordination Pd0
NL1, NL2: bridge sites of low index planes
NL3, NL4: three-fold sites of Pd(111)
Peak assignments for the catalysts analyzed by FTIR can be found in Table S1. In the case of Pd/SiO2 (hd), the linear region was deconvoluted into four bands centered at 2113, 2094, 2065 and 2042 cm-1, and the non-linear region was deconvoluted into four bands centered at 1971, 1952, 1890 and 1816 cm-1. In the case of Pd/SiO2 (ld), the linear region was deconvoluted into two bands at 2091 and 2066 cm-1, while the non-linear region was deconvoluted into four bands at 1973, 1939, 1891 and 1833 cm-1.Following Au deposition, peak shifts to lower frequencies are generally observed and the peak intensities decrease(2).
3 Additional reactivity data
Table S2. Decomposition of H2O2 (ld catalysts) using a 2wt% H2O2 feed solution in 1:1 molar MeOH:H2O. H2 conversion was determined by gas chromatography before/after reaction. Batch conditions: 278 K: 2.9 MPa 5% H2/CO2; stir rate 1500 rpm.
H2O2 conversion (%) / H2O2 decomposeda (%) / H2O2decomposedb (%)Pd/SiO2 (ld) / 39 / 83 / 17
0.69MLAu-Pd/ SiO2 (ld) / 43 / 78 / 22
aFrom hydrogenation, based on H2 consumed.
bFromdisproportionation, based on difference between H2O2 decomposed and H2 consumed.
4 Evaluation of mass transfer limitations
Figure S1. Effect of stirring speed on H2 conversion and H2O2 production during H2O2 synthesis using 0.6 MLAuPd/SiO2 catalyst (ld). Batch conditions: 278 K; 2.9 MPa 5% H2/CO2 + 1.2 MPa 25% O2/CO2; 12g of 1:1 molar MeOH:H2O;12 mg catalyst;20 minutes reaction time.
Figure S2. H2 conversion (●), selectivity to H2O2 (□) and mmol of H2O2 produced (■) vs mass of 0.69MLAuPd/SiO2 catalyst (ld) used in the reaction.Batch conditions: 278 K; 2.9 MPa 5% H2/CO2 + 1.2 MPa 25% O2/CO2; 12g 1:1 molar MeOH:H2O; stir rate 1500 rpm.
References
1.Zou, W., and Gonzalez, R. D. (1992) The preparation of silica supported Pd catalysts: the effect if pretreatment variables on particle size. Catal. Lett.12, 73-86
2.Rebelli, J., Detwiler, M., Ma, S., Williams, C. T., and Monnier, J. R. (2010) Synthesis and characterization of Au-Pd/SiO2 bimetallic catalysts prepared by electroless deposition. J. Catal.270, 224-233
3.Tiznado, H., Fuentes, S., and Zaera, F. (2004) Infrared Study of CO Adsorbed on Pd/Al2O3-ZrO2. Effect of Zirconia Added by Impregnation. Langmuir20, 10490-10497
1