Chemisorption Pulse titration - Homework - Silver (2.2 wt% on silica) - Surface reaction: 2Agsurf + 02 -» 2 AgOsurf @T = 170 °C (no bulk oxidation!) - msample = °-5021 8 vpuise = 0.00925 cm3 02@RT@latm Max TCD signal = 0.022 - D = ? Heterogeneous catalysis (C9981) Lecture 6 Catalysts characterization - continuation styskalik@chemi.muni.cz styskalik.sci.muni.cz Catalyst characterization • Outline - Solid state NMR techniques - Hydrophilicity vs. Hydrophobicity meas • Water sorption • Dynamic water sorption • Inverse gas chromatography • Microcallorimetry • Quartz crystal microbalance - In situ and operando techniques Solid state NMR techniques • Magic angle spinning (MAS) • Multiple quantum experiments (MQ) • Dynamic nuclear polarization (DNP) Solid state NMR techniques - Spinning averages dipolar interaction, chemical shift anisotropy, and quadrupolar interaction - "Residues" of these interactions are observed spinning sidebands - Static and double rotation NMR possible A Magic angle spinning (MAS) - 54.74 ° Solid state NMR techniques 31 polymeric product, gel molecular condensation products precursor, OP(OSiMe3)3 2h, 100 °C, SSNMR oligomeric condensation products 168 h, r.t. 48 h, r.t. ■10 ■20 ■30 -40 ■50 -60 Chemical shift [ppm] Solid state NMR techniques 13CCPMAS CH3C00 SiHexP \ I CgH^ +CH3COO Me3SiO C a> a> > a> Me3SiO + MeSi03 MeSiP CH3COO CH3COO SiP * CHoCOO yx_A. Me3Sid CH3COO T" 0 250 200 150 100 Chemical shift [ppm] 50 Solid state NMR techniques Solid state NMR techniques i-■-1-■-1-■-1-■-1-■-1 150 100 50 0 -50 -100 Chemical shift (ppm) Solid state NMR techniques Dynamic nuclear polarization (DNP) ^ n Solid state NMR techniques • Dynamic nuclear polarization (DNP) 200 150 100 50 0 13C Chemical Shift (ppm) Solid state NMR techniques Static NMR (=no spinning) 27AI isotropic chemical shift position Solid state NMR techniques Static NMR (=no spinning) 27AI triAl styskalik, 11 kHz, RTt spin echo (L1 =2) 90CT(Siq)=3.9usat200W 90CT(sot)=1.3usat200W September 2020 —I—i—i—i—i—|—i—i—i—i—|—i—i—i—i—|—i—i—i—i—|— 300 200 100 0 -100 i—i—i—i—|—i—i—i—i—|—i—r - 200 [ppm] Solid state NMR techniques Multiple quantum MAS (MQMAS) m, =-3/2 mi =-1/2 mi =+1/2 ST CT S t \ TQ m, = +3/2 —l_I__- - - CT TQ 1 Zeeman First-order quadru polar Second-order quadrupolar Solid state NMR techniques Multiple quantum MAS (MQMAS) Frydman etal., J. Am. Cftem. Soc. 117, 5367(1995) 3Q CT Solid state NMR techniques Multiple quantum MAS (MQMAS) FT Anisotropic T Isotropic /—- Shearing Solid state NMR techniques Multiple quantum MAS (MQMAS) 2D 27AI TQM AS □ □ Row : .56.92 ppm [189 of 512] -1-r^—\-1-^-1-r-1-1-f \- E n. a. 100 50 i—I—r 0 o O 00 o o ~~I-1—r-1-1— 50 F2 [ppm] Solid state NMR techniques Multiple quantum MAS (MQMAS) 2D 27AI TQM AS SYNTHESIS f.'o bnC Mo3SnO Si _-0^ OSnMe, O-Si •s>- OSnMe, f.V ,SnO / -Si 0.l-S 1 -O M.JSnO-\-^.!"^0.|-Si OSnMei L - I L I ^ R CI CI I. Al CI CI \ OSnMe3 (Me3Sn)8Si8O20 = Q) - SnMe CI or - SnMe3R • ,, % ... 27AI MQ/MAS NMR ,CH3 H,C- 0 o EJUS ®JJ& (auu§ ax O O O O o b b b b DFT 2.2 6.7 8.0 8.4 11.5 14.6 EXP 10.1 10.7 11.8 15.1 Kejik et al., Inorg. Chemv 2024, https://doi.org/10.1021/acs.inorgchem.3c04035 Hydrophilicity vs. Hydrophobicity • Why? - Remember: Adsorption/desorption step in cata as important as cata rxn itself (@Lecture 1) - Moreover: strong efforts nowadays put forward bio-sources instead of fossil fuels - Compare • Oil - long hydrocarbon chains (hydrophobic) • Wood - cellulose, lignin = sugar based materials = a lot of oxygen, OH groups (hydrophilic) Hydrophilicity vs. Hydrophobicity • Possibilities: — Water sorption — Dynamic vapor sorption/Quartz crystal microbalance — Inverse gas chromatography — Microcallorimetry Hydrophilicity vs. Hydrophobicity • Problems: - What is a measure of hydrophobicity? • A material can have high/low affinity to both water and organic molecules (i.e. if a sample is hydrophilic, it does not necessarily mean it is hydrophobic!) - % of pore volume filled with water at certain p/p0 - Hydrophobic index (water/toluene competitive sorption) - Heat of adsorption, heat of immersion a a a — Chemisorption: Do chemisorbed molecules account for hydrophobicity/philicity? Hydrophilicity vs. Hydrophobicity • Water sorption - Similar to N2 physisorption — Known volume and pressure in the cell, known mass of the sample Hydrophilic materials Hydrophobic materials V r- V III/ ( V f M ( V 1 p/p0 V i V > p/p0 / ( V ) p/p0 VII ( V / [ 1 p>p„ o p/po Fig. 1. Adsorption isotherms classified according to IUPAC: type I: very hydrophilic material, type II: hydrophilic material, type III: hydrophobic/ low hydrophilic material with weak sorbent-water interactions, type IV: hydrophilic material, type V: hydrophobic/low hydrophilic material with weak sorbent-water interactions, type VI: hydrophilic material with multiple sorbent-water interactions and stepwise sorption, type VII: very hydrophobic material. Hydrophilicity vs. Hydrophobicity Water sorption Very strong interaction water-adsorbent Strongly hydrophilic Water clustering = water-water interaction (liquefaction, condensation) stronger than water-adsorbent Strongly hydrophobic Very weak interaction water-adsorbent & - P. Ngf S~ Mint oval M icroporo us and M esop o ro us M a te rials 114 (2008) 1-26 Hydrophilicity vs. Hydrophobicity Water sorption - Plotting In p against 1/7at constant adsorption uptake gives a straight line with a slope equal to Hiso/R - Hiso = isosteric heat of adsorption - Isotherms at multiple temperatures needed! 1 Phys. Chem. C201Z, 116, 13316-13323 Hydrophilicity vs. Hydrophobicity Water sorption Hydrophobic material = very low Hiso = negligible interaction water-adsorbent 40 H c .O a. 2 id 0 1 »H - Hiso = isosteric heat of adsorption Hydrophilic material = very high Hiso = strong interaction water-adsorbent 30-1 ► Hiso more or less constant = water-water interaction (condensation) ■ H-ZSM5 (15) • NH4-ZSM5(15) * H-ZSM5 (140) T NH4ZSM5 (140) 4 Silicalite (OH) Silicalite (F") ~T~ 2 1 3 T 4 -r 5 Q (mmol/g) Hydrophilicity vs. Hydrophobicity • Dynamic vapor sorption/Quartz crystal microbalance - You deposit your material on an accurate microbalance - You expose it to vapors of different gases/liquids (water, alcohols, hydrocarbons,...) — You follow the uptake by changes of mass — If we can control/follow pressure, then isotherms can be obtained similar to a classic physisorption Hydrophilicity vs. Hydrophobicity • Inverse gas chromatography — You pack column (~ 50 cm) with the material you want to test (~ 0.5 g) -You inject series of gases/liquids (e.g. methane, ethane,...hexane, heptane; methanol, ethanol,...; benzene, toluene, xylene...) — You follow retention time (you directly see „affinity" of your material to selected liquids) — Models (math) can give surface energy,... Hydrophilicity vs. Hydr • Immersion microcalorimetry - Evacuated sample sealed in a bulb with brittle end — Bulb immersed in a testing liquid, sealed — Bulb broken (rod pushed down) - Liquid gets into the bulb, adsorbs, heat of immersion released and measured Fig. 1. Set-up for immersion calorimctry. Hydrophilicity vs. Hydrophobicity • Immersion microcalorimetry — Ti-MCM-41, pure inorganic vs. increasing degree of surface silylation (increasing carbon content) C content (wt.%) Time (in hours) Fig, 7. Evolution of the areal enthalpy of immersion (mj/m2) in methanol and 2- Fig. & Catalytic activity of Ti-MCM-41 materials with different silylation degrees metbyl-2-propane I as a function of carbon content for the different si ly la ted Ti- inthecydohexene epoxidation with TBHP (and 0.5 wtK of catalyst) at 33 3 K during MCM-41 samples. ^ fii (a)Cyclohexene Conversion (KMoL); (b) Epoxide Selectivity pMol], J. Silvestre-Albero et al. / Applied Catalysis A: General 507 (2015) 14-25 In situ and operando techniques In situ = online analysis of a working catalyst Operando = online analysis of a working catalyst at relevant conditions (p, T, WHSV) Technique Information Suitable to operando charac. IR spectroscopy (FTIR/DRIFTS/ATR/IRAS) Adsorbate nature, adsorption site ✓ Raman spectroscopy (SERS/TERS) Solid structure, adsorbate nature XAS (EXAFS/XANES/QXAS) Local environment, oxidation state ✓ SAXS (GISAXS) NP size and morphology ✓ XRD (PXRD/SXRD/HEXRD) Crystal phase and dimension ✓ XPS(NAP-XPS) Chemical composition, oxidation state Low pressure, large volume TEM (Environmental TEM) [In situ TEM) Atomic structure, chemical distribution Low pressure, large volume Low catalyst amount SPM (STM, AFM...) Surface structure Planar model catalysts In situ and operando techniques We already know these techniques, let's look at the examples! - Low energy electron diffraction (LEED, gives similar results to x-ray diffraction = analysis of crystal structures) - X-ray absorption near edge structure (XANES) - Diffusive reflectance infrared Fourier transform spectroscopy (DRIFTS) In situ and operando techniques • Example: LEED - low energy electron diffraction • Ethylbenzene dehydrogenation to styrene - 600 °C, 1 atm, 10-fold excess water vapor - Over Fe203 epitaxially grown on Pt(lll) • Flow reactor located in a high pressure cell - Heated by lasers - GC-MS analysis of catalytic products - LEED analysis enabled by gate valve (high pressure/ultra high vacuum) and sapphire window W. Weiss, R. SchlQgl / An integrated surface science approach towards, metal oxide catalysis In situ and operando techniques • Example: LEED - low energy electron diffraction PEEM chamber STM chamber Before catalytic reaction After catalytic reaction Initial period, no catalytic activity f 4 §3 3 a-Fe3O,(0001) hydrogen xO.01 ethyl benzene heater on (870 K) I Working catalyst styrent defect density - high ......medium low low medium high high medium Low 10 20 30 Time / min 40 50 In situ and operando techniques • Example: LEED - low energy electron diffraction Loss of catalytic activity In situ and operando techniques • Example: XANES - x-ray absorption near edge structure • Methanol oxidation to formaldehyde over Cu - 25-450 °C, 1 mbar - Cu in the form of polycrystalline foil 2 CH3OH + 02 -> 2 CH20 + 2 H20 In situ and operando techniques • Example: XANES - x-ray absorption near edge structure 2 CHaOH + O, -> 2 CH-,0 + 2 hkO Catalytic Activity 0.4 d.6 a.a Row ratio O 2 / ChfeOH n situ and operando techniques • Example: XANES - x-ray absorption near edge structure 10 h co (U S 6 (Ľ S 4 -2 O K-edge Tempe rati 531.6 ev Flow ratio 02/CH3OH 670 K 670 K 570 K 300 K Reference Cli20 ........i i i i less active very active 2 oxide and 1 suboxide species 520 530 540 550 560 570 Photon Energy / eV In situ and operando techniques Example: XANES - x-ray absorption near edge structure ~ 720 K • Positive correlation between 670 K t |-A-1 T, / , / X 620 K catalytic activity and Cu suboxide 570K T / species • Explanation/idea/description of f 520 K active species: Subsurface oxygen cover by a strained layer of copper / 485 K atoms 1—4H / 470 K / • Results confirmed by near ambient /h-#H 420 K i i i i pressure XPS (NAP XPS) 0.4 0£ 0.8 Integrated intensity (norm, u) In situ and operando techniques • Example: DRIFTS - diffuse reflectance infrared Fourier transform spectroscopy • Coupling of ethanol and acetaldehyde to 1,3-butadiene overTa doped zeolite - 300 °C, 1 atm - Well dispersed (virtually isolated) Ta sites 2 C2H5OH + CH3CHO -> C4H6 + 2 H20 DOh KM021/acscatal.6bQ1642 ACÍ Carol 2016, 6, 6323-6332 In situ and operando techniques • Example: DRIFTS - diffuse reflectance infrared Fourier transform spectroscopy Scheme 2. Schematic Overview of the DRIFTS-MS Setup" Time Time Time Scheme 2. Schematic Overview of the DRIFTS-MS Setup" Time Time Time *TBy using two syringe pumps and heated coils that enter a two-position—four-way valve, the gas-phase composition can be modulated between substrates A and B. Depending on the chosen position, either flow A or B flows through the DRIFTS accessory followed by the online mass spectrometer. In addition, two three-way valves allow the substrates to bypass the DRIFTS accessory to ensure steady gas-phase concentrations prior to measurements. In situ and operando techniques • Example: DRIFTS EtOH AA AOL CA COH OH |-H2 Table L Chosen m/z Signals" and Some 1R Vibrational Frequencies'* for the Most Important Intermediates Molecule m/z C-H stretch [cm-1] c=o stretch c=c stretch [cm-1] other vibrations [cm-1] EtOH 46 2988, 2970, 2900 106S AA II 2820, 2725, 2700 1750 BD 54 3108, 3090, 3045 1605, 1588 CA 70 2935, 2820, 2730 1722, 1710 1640 COH 57 3025, 2937, 2880 1676 1450, 1440 In situ and operando techniques • Example: DRIFTS - diffuse reflectance infrared Fourier transform spectroscopy