Operando thermal analysis - PDF Free Download

Operando thermal analysis Andrey Tarasov 8.12.2017 Andrey Tarasov, FHI MPG 1

Terms and Definitions Definition of TA Group of physical-chemical methods which deal with studying materials and processes under conditions of programmed changing's of the surrounding temperature. Thermogravimetry Differential Scanning Calorimetry M Heat flow t / T dn 1 dm r d M d m=m N A(s) B(g) Course of the reaction, yield of the reaction Key parameters: dq m C d p Q=m C p T A(s) B(s) A(s) B(g) t / T dt d Enthalpy of formation/transformation (reaction, phase transition) Andrey Tarasov, FHI MPG 2

Terms and Definitions Definition of TA Group of physical-chemical methods which deal with studying materials and processes under conditions of programmed changing's of the surrounding temperature. Thermogravimetry Differential Scanning Calorimetry M Heat flow r m=m N t / T dn 1 dm d M d dq m C d p Q=m C p T operando in-situ on site in heterogeneous catalysis in reaction mixture under operation conditions t / T dt d T, P, μ conversion/actitvity, mass transfer conditions Andrey Tarasov, FHI MPG 3

Thermogravimetry: Basic Principle S MP - Measurement signal F B - Buoyancy force, f(t) m A - Mass of adsorbed gas, f(t) m SC - Mass of sample container m S - Mass of sample, f(t) V A - Volume of adsorbed gas, f(t) V SC - Volume of sample container V S - Volume of sample, f(t) ρ gas - Density of gas, f(t) S MP g = ((m SC + m S + m A ) - (V SC + V S + V A ) ρ gas ) g Signal System mass Buoyancy Force Andrey Tarasov, FHI MPG 4

Is it sensitive enough? 1898, Marie Curie weighted radioactivity 88 Ra, 84 Po Ionisation chamber ampermeter Piezoelectric balance Marie and Pierre Curies diary, 1902. Curie Museum Mr(Ra)=225 battery mirror 1 g earth crust 10-13 g Ra Andrey Tarasov, FHI MPG 5

Thermogravimetry: Basic Principle T P S MP g = ((m SC + m S + m A ) - (V SC + V S + V A ) ρ gas ) g Signal System mass Buoyancy Force T=const? P=const S MP - Measurement signal F B - Buoyancy force, f(t) m A - Mass of adsorbed gas, f(t) m SC - Mass of sample container m S - Mass of sample, f(t) V A - Volume of adsorbed gas, f(t) V SC - Volume of sample container V S - Volume of sample, f(t) ρ gas - Density of gas, f(t) Andrey Tarasov, FHI MPG 6

Balance Schematic diagram of the Cahn Electrobalnce Commercially available thermobalances employ one of the Cahn-type electromagnetic balance Andrey Tarasov, FHI MPG 7

Temperature detection No contact Close proximity With contact Andrey Tarasov, FHI MPG 8

Sample holders Andrey Tarasov, FHI MPG 9

Sample holders Andrey Tarasov, FHI MPG 10

Thermobalance construction geometries Horizontal, parallel-guided Vertical, free suspended Mettler Toledo Vertical, top-loader TA instruments Netzsch, Setaram Rubotherm Andrey Tarasov, FHI MPG 11

Furnace Convection Currents and Turbulence Effect of furnace top opening on apparent mass-change, 5Kpm Andrey Tarasov, FHI MPG 12

TG /mg 1.0 0.5 100 Nml/min 5Kpm 15 Nml/min [12] 0.0-0.5 Normal baseline Anomaly baseline [13.1] 200 400 600 800 1000 1200 1400 Temperature / C Reproducible in different gas atmospheres and by different heating rates gas flow decreases during the heating, starting from 600 C

Reassembling the oven Top part of the tube was plugged with solid material The material was analyzed by various techniques Andrey Tarasov, FHI MPG, 14

XRD Main crystalline phase is AlF 3 Andrey Tarasov, FHI MPG, 15

XRF Formula Concentration, % AlF3 92.4 Bi2O3 0.45 CaO 0.62 Cr2O3 0.54 CuO 1.17 Fe2O3 1.69 K2O 0.55 MoO3 2.95 NiO 0.16 P2O5 0.33 Ru 0.642 SiO2 1.3 SO3 0.45 WO3 0.33 ZnO 2.21 Elemental analysis Andrey Tarasov, FHI MPG, 16

SEM_EDX Surface microstructure Andrey Tarasov, FHI MPG, 17

SEM_EDX a b c HV 7kV fig -001a a HV 20kV fig -002a Andrey Tarasov, FHI MPG, 18

DSC Reversible melting point (explains dynamic behaviour of the flow) DSC /(mw/mg) Temp. / C DSC /(mw/mg) Temp. / C exo [14] exo 550 0.75 480 0.20 0.70 T onset :450 C [14] 460 0.15 500 450 0.65 440 420 0.10 [14] 400 0.60 Q=-3.3 J/g(sample) 400 0.05 [14] 350 37 38 39 40 41 42 43 44 45 46 Time /min eutectic LiF-NaF-KF (46.5-11.5-42) T m =454 C K 1-3 AlF 4-6, CsAlF 4 (NOCOLOK ) T m =560-570 C AgF T m =435 C Zn T m = 419 C 85 90 95 100 105 110 115 120 Time /min Ammount of the phase undergoes melting 1.5-3% Andrey Tarasov, FHI MPG, 19

TG /mg 1.0 Melting and blocking the opening 0.5 [12] 0.0-0.5 Normal baseline Anomaly baseline [13.1] 200 400 600 800 1000 1200 1400 Temperature / C Andrey Tarasov, FHI MPG, 20

Nearing the plug flow conditions Andrey Tarasov, FHI MPG 21

Nearing the plug flow conditions Andrey Tarasov, FHI MPG 22

Case Study: Methanol Synthesis CO 2 + 3H 2 CH 3 OH + H 2 O ZnO Cu 250 C, 30bar CO2 3H2 CH3OH H2O H 53kJ CO 2 H2 CO H2O H 41kJ / mol CO H CH OH H 95kJ / mol 2 2 3 What is the surface composition during the operation? / mol Andrey Tarasov, FHI MPG 23

Case Study: Methanol Synthesis High Preasure Thermobalance Andrey Tarasov, FHI MPG 24

Case Study: Methanol Synthesis Reaction intermediates and spectators: H O H CH 3 O H O C O O H C O Water O H Hydroxy Methoxy H C Formyl O Carboxyl (cis) O O C O Carbonate Formate (bidentate) O C O H Formate (monodentate) Andrey Tarasov, FHI MPG 25

Case Study: Methanol Synthesis Gas Density (kg/m 3 ) CO/CO 2 /H 2 /He(6/8/59/27) 0.33 CO/Ar/H 2 /He(14/4/59/23) 0.34 CO 2 /He/H 2 (12.4/28.8/58.8) 0.35 Density alignment 105 M / % I / A 103 1.5x10-10 102 1.0x10-10 100 99 CO CO 2 /CO CO 2 5.0x10-11 97 96 0.0 3 4 5 6 7 8 9 10 time / hrs 400mg SiO 2, 30 bar, 250 C, feed gas flow 120 ml/min Andrey Tarasov, FHI MPG 26

M / % Concentration / % M / % I / A Case Study: Methanol Synthesis TG Methanol Synthesis (250 C, 30bar) Addition of 1.5% H 2 O (250 C, 1bar) 104 50 102 3x10-11 45 103 102-0.7% 40 35 30 101 100 +1.3% -0.8% 0.5% 2x10-11 101 100 99 98 +1.9% +1.2% 25 20 CO/H 2 15 CO 2 /H 2 CO 2 /H 2 CO 2 10 5 CO 0 10 15 20 25 30 35 40 t / h 99 98 85%H 2 /Ar/1.5%H 2 O m/z 18 85%H 2 /Ar 85%H 2 /Ar 97 0 10 15 20 25 30 35 40 45 t / h 1x10-11 Andrey Tarasov, FHI MPG 27

Case Study: Methanol Synthesis Cu sites 400 µmol g(cat) -1 ZnOx sites 273 µmol g(cat) -1 Schumann et al. ACS Catalysis, 2015, 5 Schumann et al. ChemCatChem, 2014, 6 Theoretical mass increase of the catalyst under estimation of full covered surface with one type of species Group/M, gmol -1 Surface stoichiometry M, % (Cu sites) M, % (ZnO sites) Full M,% (Cu/ZnO x sites) H 2 O/18 water OH/17 hydroxy OCH 3 /31 methoxy CHOO/45 formate 1 0.72 0.49 1.21 1 0.68 0.46 1.14 1 1.24 0.85 2.09 2/1 1.8/0.9 1.2/0.6 3/1.5 Andrey Tarasov, FHI MPG 28

Coverage / ML Surface Coverage ML Case Study: Methanol Synthesis Addition of 1.5% H 2 O (250 C, 1bar) TG Methanol Synthesis (250 C, 30bar) 2.0 1.50 1.5 1.25 CO 2 /H 2 CO 2 /H 2 1.0 85%H 2 /Ar/1.5%H 2 O experimental curve 1.00 CO/H 2 0.5 Cu 85%H 2 /Ar 0.75 0.50 water derived species 0.0 85%H 2 /Ar ZnO x 0.25 carbon based species 10 15 20 25 30 35 40 45 t / h 0.00 10 15 20 25 30 35 40 t / h Andrey Tarasov, FHI MPG 29

Case Study: Dry Reforming of methane CO 2 + CH 4 CO + H 2 Ni MgAl 2 O 4-x Target Reaction Dry reforming (DRM): CO 2 + CH 4 2 CO + 2 H 2 ΔH 0 = 247 kj/mol Side reactions ( catalyst deactivation because of coking): Boudouard reaction: 2 CO C + CO 2 ΔH 0 = -171 kj/mol Methane pyrolysis: CH 4 C + 2H 2 ΔH 0 = 75 kj/mol Suppression of side reactions: high reaction temperature (900 C) high temperature stable, long term active, non coking materials required Ni/MgAl 2 O 4 catalyst Andrey Tarasov, FHI MPG 30

Case Study: Dry Reforming of methane CO 2 + CH 4 2 CO + 2 H 2 ΔH 0 = 247 kj/mol Activity Weight change 4.2mmol (CH 4 )/g(cat)/s 9%wt/h 2%wt/h 3.2mmol (CH 4 )/g(cat)/s 3%wt/h Better performance at higher temperatures Continuous coke formation Andrey Tarasov, FHI MPG 31

Case Study: Dry Reforming of methane Activity in DRM Continues coking process Less coking at lower Ni concentrations Carbon formation Tarasov et al., Chem. Ing. Tech., 2014, 86, 1916-1924 Andrey Tarasov, FHI MPG 32

Definition of TA Group of physical-chemical methods which deal with studying materials and processes under conditions of programmed changing's of the surrounding temperature. Thermogravimetry Differential Scanning Calorimetry M Terms and Definitions Heat flow t / T dn 1 dm r d M d m=m N A(s) B(g) Course of the reaction, yield of the reaction Key parameters: dq m C d p Q=m C p T A(s) B(s) A(s) B(g) t / T dt d Enthalpy of formation/transformation (reaction, phase transition) Andrey Tarasov, FHI MPG 33

Terms and Definitions Differential Scanning Calorimetry (DSC) experimental methods for measuring thermal effects (heat evolution and consumption) - in extended range of temperatures; - with improved productivity; - with higher temporal resolution Differential permanently compared to reference Scanning varied (programmed) temperature (permanently and/or stepwise) Calorimetry `near calorimetric (although reduced) precision (typically, 1-2% of measured thermal value) as a rule satisactory for a wide range of applications Based on different technical principles and schemes but fundamentally same physical background: heat transfer and balance Andrey Tarasov, FHI MPG 35

Basic Principles and Terminology DSC-TG DSC - (Differential Scanning Calorimetry): Voltage to keep ΔT = T S -T R = 0 vs. T RDTA (Reverse Differential Thermal Analysis) dt/dt vs. T TG Calvet TA TA (Thermal analysis ) T S vs. t TG (Thermogravimetric analysis) Δm vs. T DTA - (Differential Thermal Analysis) ΔT = T S -T R vs. T DDTA - (Derivative DTA) dδt/dt vs. T DTA-TG Calvet-DSC Andrey Tarasov, FHI MPG 36

Basic Principles and Terminology Based on different technical principles and schemes but fundamentally same physical background: heat transfer and balance q = k T + C(dT/dt) heat removal and stortage Andrey Tarasov, FHI MPG 37

Methods and Instruments DSC Heat flux Disk shaped, Quantitative TA Calvet cell Andrey Tarasov, FHI MPG 38

Methods and Instruments 1. Quantitative TA multiple sensors tight contact between sensors and holders rapid heat removal from the sample C(dT/dt) 0 and q k T Andrey Tarasov, FHI MPG 39

Methods and Instruments 1. Quantitative TA multiple sensors tight contact between sensors and holders rapid heat removal from the sample - relatively simple design; - wide range of T s; - compatible with other methods (e.g. TG) - calibration is critical and can vary from sample to sample; - gas-solid diffusion Andrey Tarasov, FHI MPG 40

Pt-PtRh(10) point thermocouple Methods and Instruments DSC sensors Pt-PtRh(10) diskshaped thermocouple Mettler NETZSCH AuAuPd, one layer 56 thermocouples CuNi disk sensor on Ag plate. Cu/Constantan disk sensor on Si(X) waffer. Mettler Toledo Andrey Tarasov, FHI MPG 41

Methods and Instruments Thermocouples Type Composition Temperature range, K Output voltage (0 C), mv T min T max T Cu /constantan 3 670 20 J Fe/constantan 70 870 34 E chromel /constantan - 970 45 K chromel /alumel 220 1270 41 S Pt/PtRh (10) 270 1570 13 P Platinel/AuPd 500 1400 12 C W/WRe(26) - 2670 39 N Nicrosil/Nisil - 1200 39 Constantan - 58% Cu, 42% Ni Chromel 89% Ni, 10% Cr, 1%Fe Alumel 94% Ni, 2% Al, 1,5% Si, 2,5 % Mn Nicrosil/Nisil Ni, Cr, Silicon/Ni, Silicon Platinel 55% Pd, 31% Pt, 14% Au μ sensor Cu/Constantan disk sensor on Si(X) waffer. τ sensor CuNi disk sensor on Ag plate. Pt-PtRh(10) diskshaped thermocouple Andrey Tarasov, FHI MPG 42

Basic Principles and Terminology 2. Heat-flux, or heat-conductive, or Calvet-type DSC heat flux is measured outside of the sample assuming that it is proportional to the T on different distances from it Calvet calorimetry (incl. DSC): - none of the TC s measures the temperature of the sample (!!!); - the DSC signal is formed as T between two cylindrical surfaces (inner and outer) on different distances from the sample Andrey Tarasov, FHI MPG 43

the sample does not play the role of thermal resistance ; no tight contact between sample (and reference) holder(s) and the sensor is required; 3D heat sensing; good gas-solid mass-transfer conditions; high compatibility (e.g. with TGA) relatively low temporal resolution 3D vs. 2D sensing: more efficient (complete) capturing of heat fluxes from/to the sample lower sensitivity to the sample properties!!! Andrey Tarasov, FHI MPG 45

Concept q = K T + C T t K ΔT + τ dδt dt - Tian equation heat removal and storage q heat flux at every moment of time K specific thermal conductivity C specific thermal capacity τ- K/C characteristic time constant Andrey Tarasov, FHI MPG 46

Concept q = k T + C(dT/dt) k T + C(d T/dt)= k[ T + *(d T/dt)] * = C/k time constant of fluxmeter Time constant is depended on design, construction and materials of the calorimetric cell. Andrey Tarasov, FHI MPG 47

Concept q = k[ T + *(d T/dt)] k * ( C/k) q @ * k * ( C/k) q @ * Andrey Tarasov, FHI MPG 48

Concept Three ranges of characteristic times of the process should be considered: τ Ө <0.1 τ τ Ө >τ Thermal inertia of the registration system completely shades the kinetics When the kinetics may rather accurately be determined using Tian equation 0.1 τ<τ Ө < τ When the available methods give kinetics that is somewhat distorted by the thermal inertia of a sample Andrey Tarasov, FHI MPG 49

In-situ DSC Andrey Tarasov, FHI MPG 50

In-situ DSC setup 0.4cm 15cm 2cm 1cm Andrey Tarasov, FHI MPG 51

In-situ DSC setup GC + MS q = dq dt / dn dt Sinev et al. Andrey Tarasov, FHI MPG 52

In-situ DSC setup Inlet 1cm 2cm Outlet Andrey Tarasov, FHI MPG 53

In-situ DSC setup 2cm 1cm With quartz tube Without quartz tube Andrey Tarasov, FHI MPG 54

What can we measure? Activation barrier Simplified schematic representation E eq(a) E app Gas state H A ads H # H r Product state H ads B Transformation of gas phase molecules Information on reaction kinetics (Ea) Simulation of different conditions in-situ Adsorption - desorption enthalpies Adsorbed state E eq(α) Phase α Deficient Phase α active state H # adaptive state reactivated H relx H r Deactivated Phase β Transformation in solid state Redox dynamics Effects of oxygen diffusion into subsurface Redestribution of bulk and surface oxygen Oxygen binding energy (oxides) Thermochemistry of defects formation Adapted using: van Santen, R. A., Modern Heterogeneous Catalysis, Wiley, 2017 and Schlögl, R., Introduction to Heterogeneous Catalysis, Lecture, FHI Berlin, 2017 Andrey Tarasov, FHI MPG 55

Q / J/s/g Case study: Validation, C 2 H 4 adsorption on Ag catalyst 5%Ag/SiO2, Max Lamoth -22-24 -26-28 -30-32 -34-36 -38-40 -42-44 -46 exo In-situ DSC 30 C, total flow 30mlm, Ptotal 1,15bar 12 hours SynAir 300 C He (*1/15) C 2 H 4-48 20 40 120 140 time / min H ads =-94kJ/mol(C 2 H 4 ) N(C 2 H 4 )=26µmol/g(cat) reversible heat flow I / A Microcalo 40 C, Prange 0-3mbar 3 hours SynAir 300 C H ads =-87-33kJ/mol(C 2 H 4 ) N(C 2 H 4 )=33µmol/g(cat) reversible Andrey Tarasov, FHI MPG 56

Q / J/s/g Q / kj/mol(c2h4) Case study: Validation, C 2 H 4 adsorption on Ag catalyst 5%Ag/SiO2, Max Lamoth -25 In-situ DSC 30 C, total flow 30mlm, P total 1.15bar, P C2H4 0.6mbar 12 hours SynAir 300 C exo heat flow He (*1/15) I / A 100.0 90.0 80.0 Microcalo 40 C, Prange 0-3mbar 3 hours SynAir 300 C 70.0-30 -35 C 2 H 4 60.0 50.0 40.0 Low energy centers may not be concerned in the flow conditions 30.0-40 25 30 35 40 45 time / min H ads =-94kJ/mol(C 2 H 4 ) N(C 2 H 4 )=26µmol/g(cat) reversibile 20.0 10.0 0.000 0.005 0.010 0.015 0.020 0.025 N (C2H4) / mmol/g 0.030 0.035 H ads =-87-33kJ/mol(C 2 H 4 ) N(C 2 H 4 )=33µmol/g(cat) reversibile Andrey Tarasov, FHI MPG 57

Q / J/s/g Q / kj/mol(c2h4) Case study: Validation, C 2 H 4 adsorption on Ag catalyst 5%Ag/SiO2, Max Lamoth -25 In-situ DSC 30 C, total flow 30mlm, P total 1.15bar, P C2H4 0.6mbar 12 hours SynAir 300 C exo heat flow He (*1/15) I / A 100.0 90.0 80.0 Microcalo 40 C, Prange 0-3mbar 3 hours SynAir 300 C 70.0-30 -35 C 2 H 4 60.0 50.0 40.0 Low energy centers may not be concerned in the flow conditions 30.0-40 25 30 35 40 45 time / min 20.0 10.0 0.000 0.005 0.010 0.015 0.020 0.025 N (C2H4) / mmol/g 0.030 0.035 Desorption and readsorption are occurring simultaneously with diffusion In UHV systems diffusion takes part in a very limited extent, while readsorption can be avoided using sufficiently high pumping speed Andrey Tarasov, FHI MPG 58

Case study: alkane ODH over VSb/Al2O3 C n H 2n+2 + ½ O 2 C n H 2n + H 2 O C n H 2n+2 + zo 2 nco X + (n+1) H 2 O Catalysts V-containing bulk and supported oxides Classical Red-Ox Kinetics over V-containing catalysts Mars-van-Krevelen* or oxygen rebound-replenish (ORR) mechanism [O] S + A [ ] S + AO [ ] S + O 2 [O] S Sinev et al. Andrey Tarasov, FHI MPG 59

C n H 2n+2 + ½ O 2 C n H 2n + H 2 O Case study: alkane ODH over VSb/Al2O3 V(4+) state is optimal for high selectivity to ethylene V(5) V(4+) jump of S @ small variations of E [O] ; V(4+) (V3+) slow decrease of S in a wide range of E [O] variation Chemical factor (i.e. state of surface sites and their interaction with HC s) Sinev et al. is more important than energy one Andrey Tarasov, FHI MPG 60

Case study: alkane ODH over VSb/Al2O3 ( H f ) M2OX-1 ( H f ) M2OX E [O] Sb 2 O 5 Sb 2 O 4 + ½ O 2-171 kj/mole O 2 Sb 2 O 4 Sb 2 O 3 + ½ O 2-383 kj/mole O 2 V 2 O 5 V 2 O 4 + ½ O 2-224 kj/mole O 2 V 2 O 4 V 2 O 3 + ½ O 2-442 kj/mole O 2 V 2 O 3 2VO + ½ O 2-710 kj/mole O 2 Is E [O] ( H f ) M2OX-1 ( H f ) M2OX??? Sinev et al. Andrey Tarasov, FHI MPG 61

Experimental approaches D[O] (endo) M 2 O X M 2 O X-1 Phase A O-deficient Phase A Hrel (exo) ( H f )M 2 O X-1 ( H f )M 2 O X (endo) M 2 O X-1 Phase B D [O] O-binding energy (in phase homogeneity range); ( H f ) M 2OX, ( H f ) M 2OX-1 standard (tabulated) values; H rel enthalpy of relaxation (elimination of vacancies, lattice re-organization, etc.) Sinev et al. ( H f )M 2 O X-1 ( H f )M 2 O X < E [O] < D [O] Experimentally measured value Andrey Tarasov, FHI MPG 62