2) Characterization P7

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1 Supporting Information Platinum and Other Transition Metal Nanoclusters (Pd, Rh) Stabilized by PAMAM Dendrimer as Excellent Heterogeneous Catalysts: Application To the methylcyclopentane (MCP) Hydrogenative Isomerisation Christophe Deraedt,, Gérôme Melaet, Walter T. Ralston,, Rong Ye,, Gabor A. Somorjai *,, Department of Chemistry, University of California Berkeley, Berkeley, California 94720, United States. Chemical Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States Table of content 1) Syntheses of all the catalysts.p2 a) Synthesis of PtNP stabilized by PAMAM dendrimer b) Synthesis of support (SBA-15) c) Synthesis of PtNP stabilized by PAMAM dendrimer supported on SBA-15 d) Synthesis of RhNP stabilized by PAMAM dendrimer and Rh/SBA-15 e) Synthesis of PdNP stabilized by PAMAM dendrimer and Pd/SBA-15 f) Synthesis of AuNP stabilized by PAMAM dendrimer and Au/SBA-15 g) Synthesis of CuNP stabilized by PAMAM dendrimer and Cu/SBA-15 2) Characterization P7 a) Transmission Electron Microscopy TEM b) Nitrogen physisorption at 77K c) X-ray Spectroscopy EXAFS d) Inductively Coupled Plasma Optical Emission Spectroscopy ICP-OES e) Ethylene hydrogenation: 3) Catalytic tests...p8 4) PtNPs TEM images and stability over high temperature.p9 a) PtNPs TEM images b) TGA analysis of SBA-15 alone and Pt/SBA-15 5) Selectivity of isomers for Pt20/SBA-15, Pt40/SBA-15 and Pt50/SBA-15 P13 1

2 6) Calculation of the number of active sites per catalyst..p14 7) EXAFS study P16 1) Syntheses of all the catalysts 1.a) Synthesis of nanoparticle stabilized by PAMAM dendrimer (Scheme 2 main text) The catalysts studied in the hydrogenative isomerization of MCP were synthesized in two steps. The first step consists in synthesizing the homogeneous MNPs (M= Pt, Pd, Rh, Au, and Cu) stabilized by the fourth generation G4OH PAMAM dendrimer in water solution by following Crooks method. 2b,4a The PtNPs were synthesized using a Schlenk flask containing 1.25 µmol of PAMAM G4OH (Dendritech 9.81% water solution) dissolved in 5 ml of deionized water. Subsequently, a 0.05 mmol of H 2 PtCl 4 (Sigma Aldrich, 99.9%) dissolved in 5 ml of deionized water was added to the dendrimer solution in order to achieve a ratio 40/1 of Pt atoms for one dendrimer ( mmol was used for a stoichiometry 50/1 and mmol for 20/1). The solution was degassed with argon during min, and then allowed to stir slowly for 3 days at room temperature. This time length is necessary to ensure the complete complexation of Pt(II) by the tertiary amine of the dendrimer. A partial complexation of Pt(II) would lead to a poly-dispersed size of nanoparticle after the reduction step. After 3 days of complexation, fresh sodium borohydride NaBH 4 (10 equivalents per Pt) dissolved in 2 ml of 5 C deionized water, was added dropwise to the Pt(II)/PAMAM-G4OH solution with a fast stirring. This leads to an instantaneous change of color from yellow/brown to dark black. The solution was allowed to stir 6 more hours before proceeding to the purification/washing step. The PtNPs solution was transferred into a snakeskin dialysis bag, and dialysis was conducted during 1.5 days in a flask containing 2 L of deionized water, regularly changing the water (4 times). The size and the distribution of the PtNPs were checked with a FEI Tecnai TEM at an accelerating voltage of 200 kv. The average sizes measured from the TEM image were 1.6 ± 0.2 nm for Pt40G4OH (Fig 1), 1.2 nm ± 0.3 nm for Pt20G4OH and 1.9 ± 0.2 nm for Pt50G4OH. The synthesis slightly differs when the metal is changed, see the supporting information for the detailed procedure. At this stage, the catalyst is ready for homogeneous catalysis. 1.b Synthesis of support (SBA-15) The heterogenized, i.e. supported version, of the nanoparticle stabilized by dendrimers is obtained by impregnation on mesoporous silica. As the nanoparticles are very small, and the size of PAMAM G4OH is 4.5 nm, we were able to load it inside mesoporous SBA-15 with 6-2

3 7 nm channel pores (as determined by nitrogen physisorption). For the synthesis of SBA-15, Pluronic P123 (12.0 g, BASF) was dissolved in deionized water (90 ml) and 2 M HCl (360 ml) while stirring at C for 1 h. Tetraethylorthosilicate (25.6 g, Sigma Aldrich, 98%) was added to the solution dropwise and allowed to stir for 20 h at 35 C. The solgel was aged at 100 C in an oven for 24 h. The resulting product was filtered to give a white powder, which was further washed with ethanol and deionized water (2 times). Finally, the support was dried in air at 100 C and then calcined at 550 C for 6 h. To prevent H 2 O absorption, the SBA-15 is stored in a desiccator before its use as a support. 1.c) Synthesis of nanoparticle stabilized by PAMAM dendrimer supported on SBA-15 (Scheme 2) The final supported catalyst is obtained by mixing 460 mg of SBA-15 with the nanoparticle water solution (9 ml) in an ultrasonic bath for 3 hours at room temperature, leading to 1.5 wt% Pt loading. The catalyst was centrifugated and then dry in an oven at 80 C during 2-3 days. The success of the impregnation was proved by ICP-OES, and TEM. ICP-OES revealed that the loading was 100% successful. TEM images, revealed that the size of the MNPs remain unchanged after the loading. Using this technic, we were able to produce MNPs-supported with mol%, of Pt, Rh, Pd, Cu and Au. 1.d) Synthesis of RhNP stabilized by PAMAM dendrimer and Rh/SBA-15 RhNPs were synthesized by the following: in a Schlenk flask, 1.25 µmol of PAMAM G4OH (purchased from Dendritech 9.81% water solution) was dissolved in 5 ml of deionized water, then 0.05 mmol of RhCl 3.xH 2 O (Sigma Aldrich, 99.9%) dissolved in 5 ml of deionized water. Subsequently, the Rh solution was added to the dendrimer solution in order to achieve a stoichiometry 40 atoms of Rh for one dendrimer ( mmol was used for a stoichiometry 50/1 and mmol for 20/1). The solution was degassed with argon during min, and then allowed to stir slowly overnight. This time length is necessary to ensure the complete complexation of Rh(III) to the interior tertiary amine of the dendrimer at room temperature. Then, the fresh sodium borohydride NaBH 4 (from 5 to 20 equivalents per Rh, 10 here) dissolved in 2 ml of 5 C deionized water, was added dropwise in the Rh(III)/PAMAM-G4OH solution, with a faster stirring, leading to the instantaneously change of color from orange to dark brown/black. The solution was allowed to stir 2-3 more hours before proceeding to the 3

4 purification/washing step. The RhNP solution was transferred into a snakeskin dialysis bag, and dialysis was conducted during 1.5 days in a flask containing 2 L of deionized water, with regularly changing the water (4 times). The size and the distribution of the RhNPs were checked with a FEI Tecnai TEM at an accelerating voltage of 200 kv, giving an average size of 1.68 ± nm (Fig S1a). The RhNPs were then supported on SBA-15 after 3 hours of signification as for Pt/SBA-15, the centrifugation of the catalyst plus the drying for 2-3 days in an oven at 80 C allow to obtain Rh/SBA-15 (see Fig S1b for TEM image, average size 1.93 ± 0.5, difficult to determined exactly). Fig S1. a) TEM image of unsupported RhNPs. The size has been determined on more than hundred nanoparticles. b) TEM image of Rh/SBA e) Synthesis of PdNP stabilized by PAMAM dendrimer and Pd/SBA-15 PdNPs were synthesized by the following: in a Schlenk flask, 1.25 µmol of PAMAM G4OH (purchased from Dendritech 9.81% water solution) was dissolved in 5 ml of deionized water, then 0.05 mmol of K 2 PdCl 4 (Sigma Aldrich, 99.9%) dissolved in 5 ml of deionized water. 30 ml of deionized water was added to the dendrimer solution. Subsequently, the Pd solution was added to the dendrimer solution in order to achieve a stoichiometry 40 atoms of Pd for one dendrimer ( mmol was used for a stoichiometry 50/1 and mmol for 20/1). The solution was degassed with argon during min. This time length is necessary to ensure the complete complexation of Pd(II) to the interior tertiary amine of the dendrimer at room temperature. Then, the fresh sodium borohydride NaBH 4 (from 5 to 20 equivalents per Pd, 10 here) dissolved in 2 ml of 5 C deionized water, was added dropwise in the Pd(II)/PAMAM- G4OH solution, with a faster stirring, leading to the instantaneously change of color from yellow to dark brown/black. The solution was allowed to stir 2-3 more hours before proceeding to the purification/washing step. The PdNP solution was transferred into a snakeskin dialysis bag, and dialysis was conducted during 1.5 days in a flask containing 2 L of deionized water, 4

5 with regularly changing the water (4 times). The size and the distribution of the PdNPs were checked with a FEI Tecnai TEM at an accelerating voltage of 200 kv, giving an average size of 1.58 ± 0.2 nm (Fig S2a). The PdNPs were then supported on SBA-15 after 3 hours of signification as for Pt/SBA-15, the centrifugation of the catalyst plus the drying for 2-3 days in an oven at 80 C allow to obtain Pd/SBA-15 (see Fig S2b for TEM image, average size 1.6 ± 0.3, difficult to determined exactly). Fig S2. a) TEM image of unsupported PdNPs. The size has been determined on more than hundred nanoparticles. b) TEM image of Pd/SBA f) Synthesis of AuNP stabilized by PAMAM dendrimer and Au/SBA-15 AuNPs were synthesized by the following: in a Schlenk flask, 1.5 µmol of PAMAM G4OH (purchased from Dendritech 9.81% water solution) was dissolved in 51.6 ml of deionized water. The solution was degassed with argon during 30 min M HAuCl 4 (6mL) was then added into the flash dropwise with vigorous stirring. Immediately, a 20 gold excess of freshly prepared mixture of 0.5 M NaBH 4 and 0.15 M NaOH (0 C stored) was injected dropwise into the flask with vigorous stirring. The reaction was then stirred for 3 hours, after which the solution is purified by dialysis as for the 3 other MNPs. The size and the distribution of the AuNPs were checked with a FEI Tecnai TEM at an accelerating voltage of 200 kv, giving an average size of 1.79 ± 0.6 nm (Fig S3a). The AuNPs were then supported on SBA-15 after 3 hours of signification as for Pt/SBA-15, the centrifugation of the catalyst plus the drying for 2-3 days in an oven at 80 C allow to obtain Au/SBA-15 (see Fig S3b for TEM image, average size 2.89 ± 0.5, difficult to determined exactly). 5

6 Fig S3. a) TEM image of unsupported AuNPs. The size has been determined on more than hundred nanoparticles. b) TEM image of Au/SBA g) Synthesis of CuNP stabilized by PAMAM dendrimer and Cu/SBA-15 CuNPs were synthesized by the following: in a Schlenk flask, 1.25 µmol of PAMAM G4OH (purchased from Dendritech 9.81% water solution) was dissolved in 5 ml of deionized water, then 0.02 mmol of CuSO 4.5H 2 O (Sigma Aldrich, 99.9%) dissolved in 2 ml of deionized water. 21 ml of deionized water was added to the dendrimer solution. Subsequently, the Cu solution was added to the dendrimer solution in order to achieve a stoichiometry 16 atoms of Cu for one dendrimer. The solution was degassed with argon during min. This time length is necessary to ensure the complete complexation of Cu(II) to the interior tertiary amine of the dendrimer at room temperature. Then, the fresh sodium borohydride NaBH 4 (from 5 to 20 equivalents per Cu, 10 here) dissolved in 2 ml of 5 C deionized water, was added dropwise in the Cu(II)/PAMAM-G4OH solution, with a faster stirring, leading to the instantaneously change of color from light blue to light brown. The solution was allowed to stir 1-2 more hours before proceeding to the purification/washing step. The CuNP solution was transferred into a snakeskin dialysis bag, and dialysis was conducted during 1.5 days in a flask containing 2 L of deionized water, with regularly changing the water (4 times). The CuNPs were then supported on SBA-15 after 3 hours of signification as for Pt/SBA-15, the centrifugation of the catalyst plus the drying for 2-3 days in an oven at 80 C allow to obtain Cu/SBA-15. 6

7 2) Characterization a) Transmission Electron Microscopy TEM: three to four drops of the nanoparticles solution were deposed on a TEM copper grid, after 1 night of drying (air) the samples were analyzed and the TEM images were obtained using a FEI Tecnai TEM an accelerating voltage of 200 kv. The average diameter size of the nanoparticles was determined by measuring hundred nanoparticles per sample. b) Nitrogen physisorption at 77K was used in order to determine the surface area and the pore size distribution of the mesoporous support, using ASAP 2020 from Micromeritrics. BET model was used for surface and BHJ model used for porous distribution. c) X-ray Spectroscopy EXAFS: performed at beamline at ALS (Advance Light Source) Berkeley Lawrence National Laboratory. Data were analyzed, pre-edge and normalization using the open source Athena program. d) Inductively Coupled Plasma Optical Emission Spectroscopy ICP-OES: 15mg of the heterogeneous catalysts were digested with 1.2 ml of Aqua Regia at 40 C during 6 hours ml of deionized water were added, and the resulting solution was centrifugated before ICP- OES analysis. The analyses were performed by an Optima 7000 DV Inductively Coupled Plasma Optical Emission Spectroscopy. e) Ethylene hydrogenation: Ethylene hydrogenation was used to determine the number of active sites of all our Pt NP catalysts. The samples were tested before and after their use in the MCP reaction. Ethylene hydrogenation on Pt is a structure insensitive reaction with a wellknown TOF at 25 C (i.e h -1 ). The ethylene hydrogenation reaction was performed in a home-built 4L batch reactor, a GC equipped with a A Hayasep Q packed column allows to separate ethylene from ethane. Typically, 10 torr ethylene and 100 torr hydrogen reacted over mg of Pt loaded SBA-15 at 25 C (see supporting information). 7

8 3) Catalytic tests The catalytic testing was performed using a home-built plug-flow reactor. The outlet flow is analyzed using a Hewlett Packard 5890 Gas Chromatogram (10% SP-2100 on 100/120 Supelcoport packed column) in line with a FID detector to detect the reactant, MCP, and the products. Well calibrated mass flow controllers were used to introduce the ultra-high purity H 2 (99.99%) and He vector gas. The reactant (MCP) flow was carefully calibrated at different temperatures and was introduced in the system with a syringe pump at a flow rate of ml/min (0.020 ml.min -1 in the gas phase). A total gas flow of ml.min -1 was used (10 ml.min -1 of He and 30 ml.min -1 of H 2 ). The catalysts (200 mg) with grain size between and mm were loaded in the reactor bed. The catalyst was pre-treated 1 hour at 150 C under the 40 ml.min -1 gas flow without MCP. The catalytic performances were evaluated at different temperature, for each new temperature, the system was allowed to reach steady state. An average of 5 GC injections is used to report data in the presented in this work. 8

9 4) PtNPs TEM images and stability over high Temperatures. a) PtNPs TEM images Fig S4. Pt20/SBA-15 average size 1.4 ± 0.3 nm (difficult to determine precisely). Fig S5. a) Pt50/SBA-15, average size 2.0 ± 0.2 nm. b) Pt50/SBA-15 after reaction (cycle C) size nm. 9

10 Fig S6. Pt/SBA-15 after reaction up to 225 C. Average size around 2 nm (difficult to determined precisely). b) TGA analysis of SBA-15 alone and Pt/SBA-15 10

11 7.2 TGA SBA mass (g) Temperature ( C) TGA of Pt/SBA- 15 Mass (g) Fig S7. TGA analysis of SBA-15 alone (up), and Pt/SBA-15 (down). Ramp 5.00 C/min to C, Ramp 2.00 C/min to C. Temperature ( C) 11

12 Stability of the dendrimer The dendrimer is still present during the catalysis. The Thermal stability of Pt/SBA-15 has been studied by TGA (thermogravimetry analysis) under nitrogen. TGA revealed that SBA-15 alone and Pt/SBA-15 were pretty stable even above 300 C. Pt/SBA-15 is composed of 1.5 wt % of Pt and around 2.75 wt % of dendrimer G4OH (Mw= g.mol-1), so a decomposition of the dendrimer inside Pt/SBA-15 is maybe tricky to observe with TGA. Change in catalytic activity is only observed when more cracking products are formed i.e. 250 C and 275 C for Pt/SBA-15, and 225 C for Rh/SBA-15. TEM images of Pt/SBA-15 which has conducted the reaction at 275 C show Pt aggregations explained by the decomposition of the dendrimer under these conditions as mentioned by Amiridis. Ethylene hydrogenation has been conducted on each Pt catalysts in order to know the active Pt sites inside our catalysts. The same quantification method has been used on Pt/SBA-15 after a normal cycle of 5 injections at each temperature 125 C, 150 C, 175 C, 200 C, 225 C and 250 C. The catalyst presents 44% less active sites than before the reaction, explained by the coke formation as mentioned in the beginning of the article. 12

13 5) Selectivity of isomers for Pt20/SBA-15, Pt40/SBA-15 and Pt50/SBA-15 Pt20/SBA MP 3- MP hexane 200 C 68,62% 24,62% 6,75% 225 C 60,20% 24,26% 15,55% Pt50/SBA MP 3- MP hexane 200 C 69,29% 23,62% 7,09% 225 C 58,87% 24,43% 16,70% Pt40/SBA MP 3- MP hexane 200 C 68,22% 23,67% 8,11% 225 C 59,18% 24,78% 16,05% Table S1: Selectivity over Pt catalysts. 13

14 6) Calculation of the number of active sites per catalyst. First way, by taking into account the size observed by TEM and the simple counting hard sphere model. Radius metals: r-pt = nm, r-rh= nm, r-pd= nm, r-au= nm Volume NP/Volume atom = number of atoms Volume NP without shell = Volume [(r-np)-(2r-atom)] Volume shell = Volume NP - Volume NP without shell Volume shell/volume atom = number atoms inside the shell = active sites Metal Pt Pd Rh Au r- M (nm) size- NP (nm) V- NP (m^3) 2.14 E E E E- 27 V- M (m^3) 1.05 E E E E- 29 number atoms in NP V without shell (m^3) 6.16 E E E E- 27 V- shell (m^3) 1.53 E E E E- 27 number atoms in shell % atom in shell 71.25% 72.2% 73.16% 66% Table S2. Calculation of the percentage of the number of metallic atom at the surface of a NP. The second way consists in using the ethylene hydrogenation test in order to know the number of active sites per Pt catalysts. It is known that ethylene hydrogenation is surface insensitive leading to a TOF of 10.7 s-1 at 25 C for Pt. 14

15 Figure S8. Hydrogenation of ethylene of Pt20/SBA-15, Pt40/SBA-15, Pt50/SBA-15. a) Rate constant of Pt20/SBA-15 = mol.s -1 Active sites = Pt for 2.1 mg of Pt20/SBA-15 %Pt in surface = 84.5% b) Rate constant of Pt40/SBA-15 = mol.s -1 Active sites = Pt for 2.2 mg of Pt40/SBA-15 %Pt in surface = 74% c) Rate constant of Pt50/SBA-15 = mol.s -1 Active sites = Pt for 2.8 mg of Pt50/SBA-15 %Pt in surface = 65% 15

16 7) EXAFS study Figure S9. a) Near Edge X-ray Absorption Fine Structure of Pt40/SBA-15 under air, H 2 and MCP conditions. b) Fourrier transform of EXAFS of Pt40/SBA-15 under air, H 2 and MCP conditions, in the R-space. 16

17 Figure S10. a) Near Edge X-ray Absorption Fine Structure of Pt20/SBA-15 under air, H 2 and MCP conditions. b) Fourrier transform of EXAFS of Pt20/SBA-15 under air, H 2 and MCP conditions, in the R-space. 17