January 2016 Report Real World Nanoparticle Synthesis on Model Supports Ritubarna Banerjee Grant Seuser Dr. Donna Chen Dr. John Regalbuto

Goals of the Proposal  Bridge the "synthesis gap": prepare real world catalysts on model surfaces that can be fully characterized on the atomic level by surface science techniques  Understanding the role of salts in controlling the particle sizes and size distributions

Proposed Hypotheses c)b) 20 nm 50 nm  Nanoparticles can be prepared on model planar surfaces with the same types of particle sizes and sizes distributions as on traditional powdered supports  Understanding the nucleation and growth processes for nanoparticles deposited by SEA will lead to better control of particle sizes

- Inducing surface charge on support by adjusting pH of impregnating solution support OH OH 2 + O-O- pH > PZC PZC pH < PZC [PdCl 4 ] 2- anionic complex [Pd(NH 3 ) 4 ] 2+ cationic complex metal uptake (per support PZC pH > PZC pH < PZC cation uptake anion uptake support [PdCl 4 ] 2- H2OH2O - resulting close packed monolayer of ionic complex (retaining hydration sheaths) with strong interaction with support - decreased mobility of metal atoms result in smaller catalyst particles (compared to simple impregnation) support reduction treatment Pd 0 OVERVIEW: STRONG ELECTROSTATIC ADSORPTION (SEA)

GRAPHENE OXIDE (GO) AND REDUCED GRAPHENE OXIDE (rGO) -Obtained from “Graphene Supermarket” by Graphene Laboratories Inc. -Due to time constraints of visiting VCU scholars learning SEA, graphene surface area was assumed to be theoretically 2000 m²/g -Initial PZC measurements pointed to very acidic contaminants. -Supports were washed using dialysis (24 hours in de-ionized water) and dried in an oven at 120°C GO PZC before wash: 0.25 PZC after wash: 1.77 Pore volume by H₂O filling: 1.0 mL/g rGO (not shown) PZC before wash: 1.77 PZC after wash: 4.72 Pore volume by H₂O filling: 6.4 mL/g (powder form, has lesser bulk density)

SEA EXPERIMENTS: Control experiment (pH Shift without metal) and Uptake Survey for GO -Support has very acidic PZC, having very wide pH range with negative charge on the surface -Use cationic Pd precursor – [Pd(NH₃)₄]²⁺ or PdTA -Surface loading: 1000 m²/L -Low pH uptake due to reaction of precursor with GO surface (non-SEA uptake) Scaled-up catalyst pH final: 11.2 Loading: 16.4% Pd

Pd/GO CATALYST CHARACTERIZATION X-ray diffraction XRD Particle Sizes (Scherrer Formula) Using Pd(111) peak DI: 15 nm SEA: 1.4 nm

Highly-Ordered Pyrolytic Graphite (HOPG): A Model Carbon Support 0.14 nm 0.25 nm 0.34 nm Freshly Cleaved HOPG 400 nm x 400 nm

Deposition of Pt clusters onto HOPG using Physical Vapor Deposition Physical Vapor Deposition Freshly Cleaved HOPG 400 nm x 400 nm 0.25 ML Pt on HOPG 400 nm x 400 nm STM Images

Deposition of Pt Clusters onto HOPG using SEA STM Clean HOPG surface SEA [Pt(NH3)4] 2+ STM & XPS Pt Clusters on HOPG Reduce in H 2 SEA + Reduction HOPG HOPG + Pt Clusters

SEA using [Pt(NH 3 ) 4 ] 2+ and an HOPG Support 1 hour in solution Reduce HOPG in hydrogen at 200 °C for 2 hours HOPG 100 ppm [Pt(NH 3 ) 4 +2 ] pH = 11

Experimental Plan  Deposit Pt nanoparticles on HOPG: confirm Pt deposition by XPS; particle size and distribution by STM  SEA conditions: 100 pm [Pt(NH 3 ) 4 ] 2+, pH=11, NaOH  Control experiment: HOPG exposed to SEA conditions with no Pt source, image surface with STM  Oil-free pumps have been purchased for the load lock  Pt/HOPG system will also be characterized by TEM  Samples must be thinned to be electron-transparent