Beat the Heat! First-principles based modeling of micro- and - - PowerPoint PPT Presentation

Technische Universität München

Karsten Reuter

Chemistry Department and Catalysis Research Center Technische Universität München

Beat the Heat!

First-principles based modeling of micro- and macroscopic heat dissipation in heterogeneous catalysis

Challenges across the scales

Quantitative transient and steady-state surface kinetics Self-consistent coupling to reactive flow field and appropriate heat balance Accurate (first-principles) energetics

• f individual elementary processes

Surface chemistry: adsorption, diffusion, reaction, desorption

I. Integrating first-principles microkinetics into fluid dynamical simulations: Macroscopic heat dissipation

A B

Molecular Dynamics

TS Chemical kinetics: Tackling rare-event time scales

kA→B kB→A kinetic Monte Carlo N t

B A

∑ ∑

→ →

+ − =

j j i j j i j i i

t P k t P k dt t dP ) ( ) ( ) (

EA→B EB→A

        ∆ − Γ =       =

→ → →

T k E Z Z h T k k

j i i j i j i B ) ( TS B

exp

• Transition State

Theory

First-principles kinetic Monte Carlo simulations for heterogeneous catalysis: Concepts, status and frontiers

• K. Reuter, in “Modeling Heterogeneous Catalytic Reactions: From the Molecular Process to the Technical System”,

(Ed.) O. Deutschmann, Wiley-VCH, Weinheim (2011). http://www.th4.ch.tum.de

600 K

CObr/-

pO (atm)

2

1

CObr/COcus Obr/Ocus pCO (atm)

1 10-5 105 10-5 10+5 10-15 10-10

Obr/ - CObr/COcus Obr/Ocus

Surface structure and composition in the reactive environment

• K. Reuter, D. Frenkel and M. Scheffler,
• Phys. Rev. Lett. 93, 116105 (2004)

T = 600 K, pO = 1 atm, pCO = 7 atm

2

CO oxidation at RuO2(110)

TPR Steady-state and transient parameter-free turnover frequencies

x x x x x x x x x xx x x x x x x x x

pCO (10-9 atm) Exp. Theory 0.0 1.0 2.0 3.0 6 4 2 TOFCO2 (1012 mol/cm2 s)

pO2 = 10-10 atm

350 K

• M. Rieger, J. Rogal, and K. Reuter,
• Phys. Rev. Lett. 100, 016105 (2008)
• K. Reuter and M. Scheffler,
• Phys. Rev. B 73, 045433 (2006)

Macroscopic regime: Heat and mass transfer T, pCO, pO2 T

pCO2

p

pO2 pCO Computational Fluid Dynamics: Stationary stagnation point flow Chemical source terms from 1p-kMC

• S. Matera and K. Reuter, Phys. Rev. B 82, 085446 (2010)

uinl = 1 cm/sec

Adiabatic limit: Surface heating

• S. Matera and K. Reuter, Catal. Lett. 133,156 (2009)

pO2 = 0.3 atm no heat flux

Isothermal limit: Mass transfer limitations

• S. Matera and K. Reuter, Catal. Lett. 133, 156 (2009)

T = const uinl = 1 cm/sec T = 600 K pO2 = 0.3 atm

Lateral channel flow: Surface heating and spatial variations

• S. Matera and K. Reuter, in preparation

pO2 = 0.3 atm pCO = 0.6 atm uinl = 10 cm/sec

• II. Heat dissipation:

More than just macroscale warm-up?!

Really Markov ?! ?

Showcase O2/Pd(100): 2.6eV adsorption energy released ! (at GGA/PBE level)

e-h pair excitation: Time-dependent perturbation theory

• M. Timmer and P. Kratzer,
• Phys. Rev. B 79, 165407 (2009)
• J. Meyer

and

• K. Reuter,

New J. Phys. 13, 085010 (2011)

Phonon energy sinks „from the shelf“

forces (eV/Å)

1.0 0.1 0.01

Exploiting locality: Elastic vs. chemical forces

• Adsorbate-induced

forces very short ranged !

QM/Me embedding

+

• DFT-parametrized MEAM

50x50x50 Pd atoms LAMMPS

• S. J. Plimpton, J. Comp. Phys. 117, 1 (1995)

Large-scale MM MD … with additional QM-force contributions

DFT GGA/PBE 6x3x4 (or 8x3x4) slabs CASTEP

S.J. Clark et al., Z. Kristallogr. 220, 567 (2005)

Forget Markov: Hot adatoms are alive!

( ( ( ( ) ) ) )

2 ~

B uc

T mk pA T S k π π π π

• =

= = =

Z=1.5 Å

• J. Meyer and K. Reuter, submitted

Beaten by the heat…

Detailed account of heat dissipation at macroscopic and microscopic level essential to reach predictive-quality in comprehensive (nano!) catalysis modeling

Jörg Meyer Sebastian Matera

MMM