Supporting Information First principles kinetic study on the effect of zeolite framework on 1-butanol dehydration Mathew John, Konstantinos Alexopoulos, Marie-Françoise Reyniers* and Guy B. Marin Laboratory for Chemical Technology, Ghent University, Technologiepark 914, B-9052 Gent, Belgium * Corresponding author. Tel.: +32 9 331 1735 Fax: +32 9 331 1759. E-mail: MarieFrancoise.Reyniers@ugent.be. S1
Table of Contents S1. Zeolite structure and unit cell parameter of H FAU, H ZSM 5, H ZSM 22 and H- FER optimized using the periodic DFT D method are shown in Figure S1 and Table S1. S2. Statistical thermodynamic calculation. S3. Thermodynamic correction for gas-phase species S4. Comparison with experimental observations: Comparison of simulated and experimental TOFs for butanol dehydration in H-ZSM-5 is shown in Table S2. S5. Comparison of immobile and mobile adsorbate approach: overview of mobile adsorbate approach and frequencies corresponding to translational and rotational modes shown in Table S3 and Table S4, respectively. Comparison of immobile and mobile adsorbate approach shown in Table S5 and Figure S2. S6. Ab initio based thermodynamic and kinetic parameters: Standard reaction enthalpy ( H r o ), reaction entropy ( S r o ), Arrhenius activation energies and pre-exponential factors for each of elementary step over H-FAU, H-ZSM-5, H-ZSM-22 and H-FER is listed in supporting information Tables S6, S7, S8 and S9, respectively S7. Adsorption of butanol/ether/water on zeolites: The adsorbed butanol monomer (M1), butanol dimer (D1), protonated ether (DBE*) and co-adsorbed butanol-water (C2) in H-FAU/ZSM-5/H-ZSM-22/H-FER zeolites is shown in Figure S3. S8. Transition state structures, TS-1 to TS-11 for all four zeolites are shown in Figure S4- S14, Comparison of geometric sizes of transition states for syn-elimination, antielimination and SN2 substitution is shown in Figure S15. S9. Standard free energy diagrams for direct dehydration (path A), ether formation (path B) and ether decomposition (path C) for H-FAU, H-ZSM-5, H-ZSM-22 and H- FER are shown in Figures S16-S27. The standard Gibbs free energy barriers for key activated steps corresponding to each path are listed in Table S10. Standard activation enthalpy ( H 0 ) and entropy ( S 0 ) for key activated steps corresponding to each path are shown in Figure S28 S10. Surface coverages: effect of 1-butanol conversion and feed butanol partial pressure on the surface coverage are shown in Figure S29 and Figure 30. Summary on the effect of reaction condition on the surface coverage is shown in Figure 31 S11. Analytical expression for the TOF of 1-butanol dehydration in zeolites. S12. References S2
S1. Zeolites Structure and unit cell parameters: Table S1. Unit cell parameters optimized using the periodic DFT D method for H FAU, H ZSM 5, H ZSM 22 and H FER. H FAU H ZSM 5 H ZSM 22 H FER a / pm 1740.05 2046.20 1132.93 1868.37 b / pm 1736.21 2012.03 1130.77 1419.93 c / pm 1742.39 1356.70 1542.76 1493.12 α / 59.88 90.00 90.14 89.93 β / 59.82 89.94 90.07 89.90 γ / 59.87 89.96 77.04 90.03 Figure S1: Framework structure and location of Brønsted acid site for H-FAU, H-ZSM-5, H-ZSM-22 and H-FER S3
S2. Statistical thermodynamic calculation The molecular partition function q for gas-phase species is calculated from statistical thermodynamics 1 as follows: q( V, T) q ( V, T) q ( T) q ( T) = (S.1) trans vib rot q vib, q trans and q rot correspond to vibrational, translational and rotational molecular partition function, respectively. Translational partition function q trans 3 2 2πmkBT ( V, T ) = V 2 h (S.2) Rotational partition function for non-linear molecule q rot 2 πi AI BIC 8π kbt ( T ) = 2 σ h 3 2 (S.3) Vibrational partition function considering the zero-point vibrational energy (ZPVE) to be the zero reference point q vib ( T ) = 3n 6 i 1 hν i 1 exp kbt (S.4) where, n is the number of atoms in the molecule, h is the Planck constant, k B is the Boltzmann factor, T is the temperature,ν i represent the vibrational frequencies obtained by a full hessian calculation with VASP, m is the molecular mass. For gas phase molecules, the volume V is calculated using an ideal gas equation. I A, I B, and I C are the principal moments of inertia, σ is symmetry number. S4
On the other hand, the molecular partition function for immobile surface species (q immobile ) is calculated from statistical thermodynamics as follows: q( T) q ( T) q ( T) = (S.5) immobile = vib q vib ( T ) = 3n i 1 hν i 1 exp kbt (S.6) where, n is the number of atoms considered in the partial hessian calculation, h is the Planck constant, k B is the Boltzmann factor, T is the temperature and ν i represent the vibrational frequencies obtained by a partial hessian calculation with VASP. The total ensemble partition function Q(N,V,T) is given as: [ q( V, T )] N Q( N, V, T ) = (S.7) N! where, N is the number of particles and q is the molecular partition function. Statistical thermodynamic calculation for internal energy (U), enthalpy (H), entropy (S) and Gibbs free energy (G) 1 U E DFT D2 + E ZPVE 2 lnq + kbt T = (S.8) H U+ PV= U+ RT N, V = (S.9) lnq S= kb lnq+ kbt (S.10) T N, V G = H TS (S.11) where, E DFT-D2 is energy from the DFT-D2 calculation, Q is total partition function, E ZPVE is the zero point mod es 1 vibrational energy calculated as the sum of all the molecular vibrational energies at 0K ( EZPVE = hν i ). 2 i S5
S3. Thermodynamic correction for gas-phase species The error in the calculated standard Gibbs free reaction energy can be ascribed to errors associated with the DFT method and the harmonic oscillator approximation when calculating the gas-phase reaction enthalpy and entropy. NIST database DFT-D2 Temperature: 298 K, Pressure: 101.3 kpa H 0 S 0 G 0 H 0 S 0 G 0 kj/mol kj/mol/k kj/mol kj/mol J/mol/K kj/mol 1-butanol (g) 1-butene (g) + H 2 O (g) 34.3 0.135-6.0 46 0.156-0.5 2 x 1-butanol (g) di-1-butyl ether (g) + H 2 O (g) -22.6-0.028-14.3-23.8-0.015-19.3 di-1-butyl ether (g) 1-butene (g) +1-butanol (g) 56.9 0.163 8.3 69.8 0.171 18.8 The following approach was used for the thermodynamic correction for the investigated gasphase reactions. The standard enthalpy of formation (H 0 ), standard entropy of formation (S 0 ) and heat capacity (Cp(T)) at different temperatures were obtained for each of the gas phase species (water, 1-butanol, 1-butene and di-butyl ether) from the NIST website 2. The temperature dependence of heat capacity were fitted to a third order polynomial which was then used to obtain enthalpy H (T) and entropy S (T) values at specific temperatures Cp (T) = a + bt + c't 2 + dt 3 (S.12) S T = + S.13 H(T) = H 0 + (S.14) S6
These values of H (T) and entropy S (T) were used for calculating the change in Gibbs free energy G (T) for each of the three reaction paths Path A (mechanism # m 1 -m 5 ) 1-butanol (g) 1-butene (g) + H 2 O (g) Path B (mechanism # m 6 -m 8 ) 2 x 1-butanol (g) di-1-butyl ether (g) + H 2 O (g) Path C (mechanism # m 9 -m 10 ) di-1-butyl ether (g) 1-butene (g) +1-butanol (g) The difference between the standard Gibbs free energy G 0 (T) DFT-D2 + harmonic oscillator approximation and the one calculated on the basis of NIST values 2 are used to calculate error associated with each of the paths (ε GpathA, ε GpathB and ε GpathC).. NIST database DFT-D2 Error dg 0 (500K) kj/mol dg 0 (500K) kj/mol dg 0 error (500K) 1-butanol (g) 1-butene (g) + H 2 O (g) -33.4-32.3-1.1 2 x 1-butanol (g) di-1-butyl ether (g) + H 2 O (g) di-1-butyl ether (g) 1-butene (g) + 1-butanol (g) -8.6-16.7 8.1-24.8-15.6-9.2 In order to eliminate this error along each path, the error is distributed amongst the adsorption/ desorption steps in each of the mechanisms. As seen from the following mechanisms, we need to solve a set of algebraic equations (equations S15-S24) in order to calculate errors associated with adsorption and desorption steps. As the number of independent equations is less than number of unknowns (error terms). Simplifying assumption were made to reduce number of unknowns. S7
The error for all steps involving butanol adsorption/desorption step are assumed to same. 1.e. error in elementary reaction involving adsorption of butanol on Zeolite forming butanol monomer (M1) is same as that of error in formation of dimer (D1) from (M1) A similar assumption was made for the adsorption/ desorption steps of other species. Although, G error may be different for different adsorbing species, but error associated with the adsorption/desorption of the same species is the same. For the activated steps that involved desorption of product, as most of the transition states the error associated with the gas-phase thermodynamic correction is assumed to be all present in the reverse step, with no change in the activation energy barrier and pre-exponential factor for the forward reaction. The distribution of error amongst the elementary steps involving adsorption/ desorption at 450 K is shown in Table S3-S6 of section S4. Comparison of the free energy diagram (for H-ZSM-5 at 500 K) for thermodynamic corrected (dotted lines) and the uncorrected (full line) case for different mechanisms are shown below : S8
S9
S10
S11
S12
S13
S4. Comparison with experimental observations. To validate the results of our ab initio based microkinetic model, a comparison is made with the experimental observation of Makarova et al. 3 for 1-butanol dehydration in H-ZSM-5. The microkinetic model was used to calculate the turnover frequency (TOF) for the production of dibutyl ether (DBE) and butene at their experimental conditions (400K, butanol feed mole fraction 0.7 %, total pressure of 1 bar and site time of 36.6 mol H+ s mol -1 ). Table S2 provides a comparison between current theoretical results with thermodynamic correction, our previous theoretical result without thermodynamic correction 4 and experimental TOFs for production of dibutyl ether (DBE) and butene. The inclusion of thermodynamic correction for gas-phase species (to account for errors associated with DFT and harmonic approximation) leads to significant improvement in results which are in line with the experimental results. Table S2. Comparison between current theoretical results with thermodynamic correction, our previous theoretical result without thermodynamic correction and experimental TOFs for production of dibutyl ether (DBE) and butene at 400K, butanol feed mole fraction 0.7%, total pressure of 1 bar and site time of 36.6 mol H+ s mol -1. This work Experimental 3 Ref 4 1 TOF Butene (mol /mol H+ /s) 3.5 10-5 4.1 10-5 2.5 10-6 2 TOF DBE (mol /mol H+ /s) 2.3 10-4 5.1 10-4 1.7 10-4 3 Conversion (mol %) 2.1 ~ 2 1.8 S14
S5. Comparison of immobile and mobile adsorbate approach for the physisorbed 1- butene. As seen from Table S3, 2D free translational and 1D free rotational modes were identified for physisorbed 1-butene in H-FAU, H-ZSM-5 and H-ZSM-22 by visual analysis of the vibrational modes 5, while only 2D free translational modes could be identified for physisorbed 1-butene in H-FER (with free rotation being restricted due to the location of the acid site). The harmonic frequencies corresponding to these translational and rotational modes are shown in Table S4. In the mobile adsorbate approach, these frequencies are removed from the calculation of the vibrational partition and are replaced by free translational and/or rotational contributions, as described by De Moor et al. 5 Table S3: Overview of the number of free translations and rotations considered in mobile approach for physisorbed 1-butene in different zeolites free translation molecular surface area (pm pm) free rotation number zeolite number H-FAU 2 800 800 1 H-ZSM-5 2 200 600 1 H-ZSM-22 2 200 600 1 H-FER 2 200 600 0 Table S4: List of harmonic frequencies (cm -1 ) corresponding to free translational and rotational modes of physisorbed 1-butene in different zeolites translational mode rotational mode H-FAU 17.6 71.5 16.1i H-ZSM-5 14.2 70.8 33.5 H-ZSM-22 8.7 54.3 31.9 H-FER 30.7 78.4 - A comparison of the standard physisorption entropy obtained using the immobile and mobile approach is presented in Table S5. As expected, the calculated entropy losses are significantly lower if mobile physisorption is assumed. S15
Table S5: Immobile versus mobile physisorption entropies (J mol -1 K -1 ) of 1-butene in different zeolites zeolite Immobile approach Mobile approach H-FAU -157-97 H-ZSM-5-155 -109 H-ZSM-22-158 -114 H-FER -179-149 Nevertheless, as seen from Figure S2, no significant difference was observed for 1-butanol conversion, while a marginal increase in 1-butene yield is observed at higher site time (conversion) when using mobile adsorbate approach instead of the immobile adsorbate approach. Figure S2: Comparison of immobile and mobile adsorbate approach for the physisorbed 1- butene. (Full and dotted lines correspond to result obtained using immobile and mobile adsorbate approach, respectively) S16
S6. Ab initio derived Thermodynamic and kinetic parameters Table S6:. Standard reaction enthalpy (kj/mol), reaction entropy (J/mol/K), activation energy (kj/mol), preexponential factor (s -1 ), forward reaction rate coefficient k f (s -1 ) at 450K, thermodynamic correction term on standard Gibbs free energy at 450 K (kj/mol) and equilibrium coefficient at 450K (10-2 kpa -1, 10 2 kpa or dimensionless for adsorption, desorption and surface transformation, respectively) for the elementary steps (numbered as indicated in Scheme 1 ) for H-FAU. Elementary steps H r o S r o E a(f) A f G 0 r ε G(T) k f (T) K eq (T) corr (R1) 1-BuOH(g) + * M1-121 -195-34 -0.7 9.7E+03 (R2) M1 W + 1-Butene(g) 84 197 175 6.0E+14-4 -0.7 3.1E-06 3.7E+00 (R3) W H2O(g) + * 83 156 13-0.7 3.3E-02 (R4) M1 C1 78 59 142 1.3E+14 51 0.0 3.7E-03 1.1E-06 (R5) C1 W + 1-Butene(g) 7 138-56 -0.7 3.5E+06 (R6) M1 M2 67 6 64 0.0 3.7E-08 (R7) M2 1-Butene*+ H2O(g) 33 189 69 2.7E+14-52 -0.7 2.7E+06 1.2E+06 (R8) 1-Butene* 1-Butene(g) + * 68 157-3 -0.7 2.8E+00 (R9) M2 Butoxy + H2O(g) 23 147 94 1.4E+14-43 -0.7 1.7E+03 1.2E+05 (R10) Butoxy 1-Butene* 11 43 91 5.8E+13-9 0.0 1.5E+03 1.0E+01 (R11) M1 + BuOH(g) D1-102 -176-23 -0.7 5.1E+02 (R12) D1 D2 127 19 119 0.0 1.7E-14 (R13) D2 C2+1-Butene(g) -27 172 36 4.3E+12-104 -0.7 3.1E+08 1.6E+12 (R14) C2 M1 + H2O(g) 49 143-16 -0.7 8.5E+01 (R15) D2 DBE* + H2O(g) -67 133 12 4.5E+12-126 -0.7 1.6E+11 5.7E+14 (R16) DBE* DBE(g) + * 140 206 47 9.6 2.8E-07 (R17) Butoxy + BuOH(g) C3-53 -160 19-0.7 7.7E-03 (R18) C3 DBE* (Sn2) -78-17 65 9.7E+12-70 0.0 2.6E+05 1.5E+08 (R19) C3 DBE* (Sn1) -78-17 128 2.4E+13-70 0.0 3.5E-02 1.5E+08 (R20) DBE* C4 108 57 140 8.4E+13 82 0.0 4.8E-03 3.0E-10 (R21) C4 1-Butene*+ BuOH(g) 34 163-39 0.7 2.9E+04 (R22) DBE* DBE2 73 0 73 0.0 3.1E-09 (R23) DBE2 1-Butene*+ BuOH(g) 68 219 68 1.9E+14-31 0.7 2.6E+06 2.9E+03 S17
Table S7: Standard reaction enthalpy (kj/mol), reaction entropy (J/mol/K), activation energy (kj/mol), preexponential factor (s -1 ), forward reaction rate coefficient k f (s -1 ) at 450K, thermodynamic correction term on standard Gibbs free energy at 450 K (kj/mol) and equilibrium coefficient at 450K (10-2 kpa -1, 10 2 kpa or dimensionless for adsorption, desorption and surface transformation, respectively) for the elementary steps (numbered as indicated in Scheme 1 ) for H-ZSM-5. (adapted from ref 4 including thermodynamic correction ) Elementary steps H r o S r o E a(f) A f G 0 r ε G(T) k f (T) K eq (T) corr (R1) 1-BuOH(g) + * M1-146 -192-60 -0.7 1.0E+07 (R2) M1 W + 1-Butene(g) 107 200 176 1.1E+15 17-0.7 4.0E-06 1.2E-02 (R3) W H2O(g) + * 85 150 18-0.7 1.0E-02 (R4) M1 C1 74 78 139 2.9E+14 38 0.0 2.0E-02 3.4E-05 (R5) C1 W + 1-Butene(g) 34 122-21 -0.7 3.5E+02 (R6) M1 M2 82-5 84 0.0 1.6E-10 (R7) M2 1-Butene*+ H2O(g) 28 199 53 9.0E+14-62 -0.7 6.9E+08 1.8E+07 (R8) 1-Butene* 1-Butene(g) + * 83 155 13-0.7 4.2E-02 (R9) M2 Butoxy + H2O(g) 22 165 49 3.4E+14-52 -0.7 6.5E+08 1.3E+06 (R10) Butoxy 1-Butene* 6 35 93 3.7E+13-10 0.0 5.3E+02 1.4E+01 (R11) M1 + BuOH(g) D1-126 -183-43 -0.7 1.3E+05 (R12) D1 D2 43-3 44 0.0 7.2E-06 (R13) D2 C2+1-Butene(g) 69 165 118 2.8E+14-6 -0.7 5.1E+00 5.4E+00 (R14) C2 M1 + H2O(g) 61 179-20 -0.7 2.3E+02 (R15) D2 DBE* + H2O(g) 15 157 92 1.4E+14-55 -0.7 3.0E+03 3.1E+06 (R16) DBE* DBE(g) + * 191 209 97 9.6 4.7E-13 (R17) Butoxy + BuOH(g) C3-95 -173-17 -0.7 1.0E+02 (R18) C3 DBE* (Sn2) -77-16 61 3.1E+12-70 0.0 2.6E+05 1.4E+08 (R19) C3 DBE* (Sn1) -77-16 111 8.9E+12-70 0.0 1.2E+00 1.4E+08 (R20) DBE* C4 102 51 140 2.5E+14 79 0.0 1.4E-02 6.6E-10 (R21) C4 1-Butene*+ BuOH(g) 76 173-2 0.7 1.5E+00 (R22) DBE* DBE2 63 9 59 0.0 1.6E-07 (R23) DBE2 1-Butene*+ BuOH(g) 115 215 84 1.6E+13 18 0.7 2.6E+03 6.3E-03 S18
Table S8:. Standard reaction enthalpy (kj/mol), reaction entropy (J/mol/K), activation energy (kj/mol), preexponential factor (s -1 ), forward reaction rate coefficient k f (s -1 ) at 450K, thermodynamic correction term on standard Gibbs free energy at 450 K (kj/mol) and equilibrium coefficient at 450K (10-2 kpa -1, 10 2 kpa or dimensionless for adsorption, desorption and surface transformation, respectively) for the elementary steps (numbered as indicated in Scheme 1 ) for H-ZSM-22. Elementary steps H r o S r o E a(f) A f G 0 r ε G(T) k f (T) K eq (T) corr (R1) 1-BuOH(g) + * M1-150 -192-64 -0.7 3.1E+07 (R2) M1 W + 1-Butene(g) 120 199 162 9.0E+14 30-0.7 1.5E-04 3.8E-04 (R3) W H2O(g) + * 77 151 9-0.7 1.0E-01 (R4) M1 C1 89 39 139 8.5E+13 72 0.0 5.6E-03 4.4E-09 (R5) C1 W + 1-Butene(g) 30 160-42 -0.7 8.7E+04 (R6) M1 M2 51 9 47 0.0 3.2E-06 (R7) M2 1-Butene*+ H2O(g) 62 183 88 2.9E+14-20 -0.7 1.7E+04 2.3E+02 (R8) 1-Butene* 1-Butene(g) + * 83 158 12-0.7 5.2E-02 (R9) M2 Butoxy + H2O(g) 39 139 74 5.9E+13-23 -0.7 1.4E+05 6.3E+02 (R10) Butoxy 1-Butene* 23 43 103 5.7E+13 4 0.0 6.2E+01 3.7E-01 (R11) M1 + BuOH(g) D1-124 -187-40 -0.7 5.0E+04 (R12) D1 D2 100 25 89 0.0 5.1E-11 (R13) D2 C2+1-Butene(g) 57 164 64 4.5E+11-16 -0.7 1.7E+04 9.5E+01 (R14) C2 M1 + H2O(g) 86 157 15-0.7 2.3E-02 (R15) D2 DBE* + H2O(g) -44 119 38 3.0E+12-97 -0.7 1.1E+08 2.3E+11 (R16) DBE* DBE(g) + * 195 222 95 9.6 7.5E-13 (R17) Butoxy + BuOH(g) C3-65 -161 7-0.7 1.8E-01 (R18) C3 DBE* (Sn2) -93-31 45 5.2E+12-79 0.0 2.9E+07 1.7E+09 (R19) C3 DBE* (Sn1) -93-31 74 1.1E+15-79 0.0 2.8E+06 1.7E+09 (R20) DBE* C4 100 70 151 1.4E+15 69 0.0 3.9E-03 1.1E-08 (R21) C4 1-Butene*+ BuOH(g) 82 165 8 0.7 1.1E-01 (R22) DBE* DBE2 81 20 72 0.0 4.8E-09 (R23) DBE2 1-Butene*+ BuOH(g) 101 215 91 5.7E+12 4 0.7 1.7E+02 2.5E-01 S19
Table S9: Standard reaction enthalpy (kj/mol), reaction entropy (J/mol/K), activation energy (kj/mol), preexponential factor (s -1 ), forward reaction rate coefficient k f (s -1 ) at 450K, thermodynamic correction term on standard Gibbs free energy at 450 K (kj/mol) and equilibrium coefficient at 450K (10-2 kpa -1, 10 2 kpa or dimensionless for adsorption, desorption and surface transformation, respectively) for the elementary steps (numbered as indicated in Scheme 1 ) for H-FER. Elementary steps H r o S r o E a(f) A f G 0 r ε G(T) k f (T) K eq (T) corr (R1) 1-BuOH(g) + * M1-106 -222-7 -0.7 7.2E+00 (R2) M1 W + 1-Butene(g) 75 220 158 5.4E+16-24 -0.7 2.7E-02 6.7E+02 (R3) W H2O(g) + * 77 159 6-0.7 2.5E-01 (R4) M1 C1 52 83 127 9.6E+14 14 0.0 1.8E+00 2.1E-02 (R5) C1 W + 1-Butene(g) 24 137-38 -0.7 3.2E+04 (R6) M1 M2 60 40 42 0.0 1.2E-05 (R7) M2 1-Butene*+ H2O(g) 54 161 73 1.0E+13-19 -0.7 3.0E+04 1.8E+02 (R8) 1-Butene* 1-Butene(g) + * 39 179-42 -0.7 8.0E+04 (R9) M2 Butoxy + H2O(g) 28 138 67 1.3E+13-34 -0.7 2.4E+05 1.2E+04 (R10) Butoxy 1-Butene* 26 23 85 3.5E+13 16 0.0 5.0E+03 1.5E-02 (R11) M1 + BuOH(g) D1-136 -179-55 -0.7 3.2E+06 (R12) D1 D2 21 20 12 0.0 4.5E-02 (R13) D2 C2+1-Butene(g) 62 134 151 5.4E+13 2-0.7 1.5E-04 7.9E-01 (R14) C2 M1 + H2O(g) 94 130 36-0.7 8.6E-05 (R15) D2 DBE* + H2O(g) 62 134 126 1.1E+13 2-0.7 2.5E-02 7.9E-01 (R16) DBE* DBE(g) + * 137 233 32 9.6 1.7E-05 (R17) Butoxy + BuOH(g) C3-82 -172-4 -0.7 4.0E+00 (R18) C3 DBE* (Sn2) -60-30 58 5.3E+12-46 0.0 9.9E+05 2.1E+05 (R19) C3 DBE* (Sn1) -60-30 97 1.4E+13-46 0.0 7.0E+01 2.1E+05 (R20) DBE* C4 55 58 116 2.4E+14 29 0.0 7.3E+00 4.8E-04 (R21) C4 1-Butene*+ BuOH(g) 113 167 37 0.7 3.8E-05 (R22) DBE* DBE2 31 34 16 0.0 1.5E-02 (R23) DBE2 1-Butene*+ BuOH(g) 136 192 131 1.2E+10 50 0.7 6.7E-06 1.3E-06 S20
S7. Adsorption of butanol/ether/water on Zeolites Figure S3: The adsorbed butanol monomer (M1 ), butanol dimer (D1), protonated ether (DBE*) and co-adsorbed butanol-water (C2) in H-FAU/ZSM-5/H-ZSM-22/H-FER zeolites. S21
S8. Transition state structures (TS): Figure S4. Transition state (TS-1) for conversion of 1-butanol monomer (M1) to 1-butene and adsorbed water (W) via E1-elimination (step 2 of mechanism m 1 ) over H-FAU/H-ZSM- 5/H-ZSM-22/H-FER. Color code: silicon - light blue, aluminum - pink, oxygen - red, hydrogen - white, carbon - grey, hydrogen bonds (distance < 250 pm) blue lines, bond breaking/forming - black lines. S22
Figure S5. Transition state (TS-2) for conversion of M1 (1-butanol monomer) to C1 (butanol and water on zeolite ) via syn-elimination (step 4 of mechanism m 2 ) over H-FAU/H-ZSM- 5/H-ZSM-22/H-FER.Color code: silicon - light blue, aluminum - pink, oxygen - red, hydrogen - white, carbon - grey, hydrogen bonds (distance < 250 pm) blue lines, bond breaking/forming - black lines. S23
Figure S6. Transition state (TS-3) for conversion of reoriented 1-butanol monomer (M2) to 1- butene and H 2 O via anti-elimination (step 7 of mechanism m 3 ) over H-FAU/H-ZSM-5/H- ZSM-22/H-FER.Color code: silicon - light blue, aluminum - pink, oxygen - red, hydrogen - white, carbon - grey, hydrogen bonds (distance < 250 pm) blue lines, bond breaking/forming - black lines. S24
Figure S7: Transition state (TS-4) for conversion of reoriented 1-butanol monomer (M2) to 1-butoxide and H 2 O via SN2 type substitution ( step 9, common to mechanism m 4/ m 7 and m 8 ) over H-FAU/H-ZSM-5/H-ZSM-22/H-FER.Color code: silicon - light blue, aluminum - pink, oxygen - red, hydrogen - white, carbon - grey, hydrogen bonds (distance < 250 pm) blue lines, bond breaking/forming - black lines. S25
Figure S8: Transition state (TS-5) for deprotonation of 1-butoxide to 1-butene (step 10 of mechanism m 4, over H-FAU/H-ZSM-5/H-ZSM-22/H-FER. Color code: silicon - light blue, aluminum - pink, oxygen - red, hydrogen - white, carbon - grey, hydrogen bonds (distance < 250 pm) blue lines, bond breaking/forming - black lines. S26
Figure S9. Transition state (TS-6) for conversion of reoriented 1-butanol dimer (D2) to 1butene,co-adsorbed butanol and H 2 O via syn-elimination ( step 13 of mechanism m 5 ) over H-FAU/H-ZSM-5/H-ZSM-22/H-FER.Color code: silicon - light blue, aluminum - pink, oxygen - red, hydrogen - white, carbon - grey, hydrogen bonds (distance < 250 pm) blue lines, bond breaking/forming - black lines. S27
Figure S10. Transition state (TS-7) for conversion of reoriented 1-butanol dimer (D2) to di-1- butyl ether (DBE*) and H 2 O via SN2 type substitution ( step 15 of mechanism m 6 ) over H- FAU/H-ZSM-5/H-ZSM-22/H-FER.Color code: silicon - light blue, aluminum - pink, oxygen - red, hydrogen - white, carbon - grey, hydrogen bonds (distance < 250 pm) blue lines, bond breaking/forming - black lines. S28
Figure S11. Transition state (TS-8) for conversion of butanol and 1-butoxide (C3) to di-1- butyl ether (DBE*) via SN2 type substitution ( step 18 of mechanism m 7 ) over H-FAU/H- ZSM-5/H-ZSM-22/H-FER.Color code: silicon - light blue, aluminum - pink, oxygen - red, hydrogen - white, carbon - grey, hydrogen bonds (distance < 250 pm) blue lines, bond breaking/forming - black lines. S29
Figure S12. Transition state (TS-9) for conversion of butanol and 1-butoxide (C3) to di-1- butyl ether (DBE*) via SN1 type substitution (step 19 of mechanism m 8 ) over H-FAU/H- ZSM-5/H-ZSM-22/H-FER.Color code: silicon - light blue, aluminum - pink, oxygen - red, hydrogen - white, carbon - grey, hydrogen bonds (distance < 250 pm) blue lines, bond breaking/forming - black lines. S30
Path C ( TS-10) Figure S13: Transition state (TS-10) for conversion of adsorbed di-1-butyl ether (DBE*) to co-adsorbed 1-butene and butanol (C4) via syn-elimination (step 20 of mechanism m 9) over H- FAU/H-ZSM-5/H-ZSM-22/H-FER. Color code: silicon - light blue, aluminum - pink, oxygen - red, hydrogen - white, carbon - grey, hydrogen bonds (distance < 250 pm) blue lines, bond breaking/forming - black lines. S31
Figure S14: Transition state (TS-11) for conversion of re-oriented adsorbed di-1-butyl ether (DBE2) to adsorbed 1-butene and butanol (g) via anti-elimination (step 23 of mechanism m 10) over H-FAU/H-ZSM-5/H-ZSM-22/H-FER. Color code: silicon - light blue, aluminum - pink, oxygen - red, hydrogen - white, carbon - grey, hydrogen bonds (distance < 250 pm) blue lines, bond breaking/forming - black lines. S32
Figure S15 : Comparison of transition state geometric size for syn,/anti-elimination and SN2 reaction (all dimensions in pm) S33
S9. Standard free energy diagram for butanol dehydration on zeolites Energy Diagram for H-FAU zeolite at 450K Figure S16: Standard Gibbs free energy for 1-butanol dehydration to 1-butene (path A) in H-FAU at 450K Figure S17: Standard Gibbs free energy for 1-butanol dehydration to di-1-butyl ether (path B) in H-FAU at 450K Figure S18: Standard Gibbs free energy for ether decomposition reaction (path C) in H-FAU at 450K S34
Energy Diagram for H-ZSM-5 zeolite at 450K Figure S19: Standard Gibbs free energy for 1-butanol dehydration to 1-butene (path A) in H-ZSM-5 at 450K Figure S20: Standard Gibbs free energy for 1-butanol dehydration to di-1-butyl ether (path B) in H-ZSM-5 at 450K Figure S21: Standard Gibbs free energy for ether decomposition reaction (path C) in H-ZSM-5 at 450K S35
Energy Diagram for H-ZSM-22 zeolite at 450K Figure S22: Standard Gibbs free energy for 1-butanol dehydration to 1-butene (path A) in H-ZSM-22 at 450K Figure S23: Standard Gibbs free energy for 1-butanol dehydration to di-1-butyl ether (path B) in H-ZSM-22 at 450K Figure S24: Standard Gibbs free energy for ether decomposition reaction (path C) in H-ZSM-22 at 450K S36
Energy Diagram for H-FER zeolite at 450K Figure S25: Standard Gibbs free energy for 1-butanol dehydration to 1-butene (path A) in H-FER at 450K Figure S26: Standard Gibbs free energy for 1-butanol dehydration to di-1-butyl ether (path B) in H-FER at 450K Figure S27: Standard Gibbs free energy for ether decomposition reaction (path C) in H-FER at 450K S37
Table S10: The standard Gibbs free energy barriers for direct dehydration of butanol ( G 0 A = G 0 TS3-M1, ether formation ( G 0 B = G 0 TS7-D1 and ether decomposition ( G 0 C = G 0 TS10-DBE ) over H-FAU, H-ZSM-5, H-ZSM- 22 and H-FER. (see Figure 4 for the standard Gibbs free energy profile). G 0 M1ads G 0 A = G TS3 G M1 G 0 D1ads G 0 B = G TS7 G D1 G 0 C = G TS10 G DBE* (kj/mol) (kj/mol) (kj/mol) (kj/mol) (kj/mol) H-FAU -34 121-56 134 132 H-ZSM-5-59 120-103 127 128 H-ZSM-22-64 123-103 131 132 H-FER -7 116-62 137 105 Figure S28 : Standard activation enthalpy ( H 0 ) and entropy ( S 0 ) of direct dehydration of butanol (butanol monomer (M1) to TS-3, mechanism m 3 of path A), ether formation (butanol dimer (D1) to TS-7, mechanism m 6 of Path B) and ether decomposition path (adsorbed di butyl ether DBE to TS-7, mechanism m 9 of path C) over H-FAU, H-ZSM-5, H- ZSM-22 and H-FER. S38
S10. Surface coverages Figure S29: Effect of 1-butanol conversion on the surface coverage of adsorbed 1-butanol monomer M1 ( ), dimer D1 ( ), di-1-butyl ether DBE* ( ), water W ( ) and free sites θ* ( ) for different zeolites at reaction temperature of 450K and butanol partial pressure of 10 kpa (these results correspond to plug-flow reactor simulations (Eqs. 3-5) with the ab-initio based microkinetic model. See Tables S3, S4, S5 and S6, for H-ZSM-5, H-FAU, H-ZSM-22 and H-FER, respectively, for the model parameters) S39
Figure S30 : Effect of 1-butanol partial pressure on surface coverage of adsorbed 1-butanol monomer M1 ( ), dimer D1 ( ), di-1-butyl ether DBE* ( ), water W ( ) and free sites θ* ( ) for different zeolites at reaction temperature of 450K and 1-butanol conversion of 10%. (these results correspond to plug-flow reactor simulations (Eqs. 3-5) with the ab-initio based microkinetic model. See Tables S3, S4, S5 and S6, for H-ZSM-5, H-FAU, H-ZSM-22 and H- FER, respectively, for the model parameters) S40
Figure 31: Summary on the effect of reaction temperature and butanol partial pressure on the surface coverage of adsorbed 1-butanol monomer M1 ( ), dimer D1 ( ), di-1-butyl ether DBE* ( ) at constant conversion of 10 %.(these results correspond to plug-flow reactor simulations (Eqs. 3-5) with the ab-initio based microkinetic model. See Tables S3, S4, S5 and S6, for H-ZSM-5, H-FAU, H-ZSM-22 and H-FER, respectively, for the model parameters) S41
S11. Analytical expression for the TOF of 1-butanol dehydration in zeolites Derivation of simplified analytical equation for path A, path B and path C. Site balance: θ +θ +θ +θ +θ +θ +θ +θ +θ +θ +θ +θ =1 (S25) where, θ is the fraction coverage for i th surface species. A detailed microkinetic simulation for all the four zeolites indicates that M1, D1 and DBE* are the key surface species and depending upon the reaction condition one of them becomes the most abundant reaction intermediates (MARI). Moreover, under the simulated range of conditions (temperature 400-450K, 1-butanol partial pressure 10-3 to 100 kpa and conversion less than 30%) the summation of surface converges of M1, D1, DBE* and θ ~1. Accordingly, the site balance equation simplifies to: θ +θ +θ +θ =1 (S26) Based on quasi steady state assumption and site balance we can derive the values for surface coverages of each species as θ = K 1 P BuOH θ θ = K 1 K 11 (P BuOH ) 2 θ (S27) (S28) θ = K -1 16 (P BuOH ) 2 θ (S29) Equation S26 becomes : θ +K 1 P BuOH θ + K 1 K 11 (P BuOH ) 2 θ + K -1 16 (P BuOH ) 2 θ =1 (S30) Which gives θ = (S31) TOFs for each path are obtained by summing up the contributions from all the mechanisms associated with each of the paths. TOF, is obtained by summing up the contributions from each of the 5 mechanisms (m 1 - m 5 ) and is given as : TOF = TOF +TOF +TOF +TOF +TOF (S32) TOF, is obtained by summing up the contributions from each of the 3 mechanisms (m 6 - m 7 ) and is given as : TOF = TOF +TOF +TOF (S33) S42
As the mechanism m 6 remain dominant for most of the reaction conditions the equation becomes: TOF = TOF (S34) TOF, is obtained by summing up the contributions from each of the 3 mechanisms (m 6 - m 8 ) and is given as : TOF = TOF +TOF +TOF (S35) As the mechanism m 6 remain dominant for most of the reaction conditions the equation becomes: TOF = TOF (S36) TOF, is obtained by summing up the contributions from mechanism m 9 and m 10 is given as : TOF = TOF +TOF (S37) A simplified form of equation can be derived for conversion x= 0, as the contribution from backward (reverse ) reaction is zero TOF =0 =k θ = K k P θ TOF =0 =k θ = K k P θ TOF =0 =k θ = K K k P θ TOF =0 =γk θ =γ K K k P θ (S38) (S39) (S40) (S41) where γ is the fraction of butoxide that gets converted into butene and is given as the ratio of the TOF for formation of butene and ether from butoxide (γ= ). TOF =0 =k θ = K K K k P θ θ (S42) Thus the TOF at zero conversion is given as : TOF at X= 0 = K k +K k +K K k +K K k γ P +K K K k P 1+ K P + K K P S43 Similar approach is used for formulating TOF expression for path B and path C. S43
These simplified analytical expression can serve as a tool for easy comparison of theoretical TOFs with that obtained from experimental measurements of initial reaction rates. At extremely low P BuOH and high temperature (K 1 and K 11 decrease with increase in temperature), free sites are much more abundant than M1 and D1, i.e. K K P + K 1 P BuOH < 1, and a first order dependence of TOF path A on P BuOH is expected (based on equation S.43) : TOF = K k +K k +K K k +K K k γ P S.44 A region of positive order pressure dependence for path A is seen for H-FAU and H-FER (see Figure 3c ) at very low butanol partial pressure (P BuOH below 10-2 kpa). At moderate and high P BuOH, K K P and K 1 P BuOH > > 1, leading to: TOF = k +k +K k + K k γ +K K k P 1+ K P S.45 Here, a negative reaction order is seen with increasing butanol partial pressure (ascribed to the P independent term in the numerator corresponding to monomolecular path A mechanisms) followed by a regime of constant TOF = K k. A negative order pressure dependence is seen for all four zeolites at moderate to high pressure (see Figure 3c) and is consistent with the experimental observation of Chiang and Bhan 6 for ethanol dehydration within zeolites and of Macht et al. for 2-butanol dehydration on POM 7. Within the range of our simulation, a zero order pressure dependence is clearly seen for H-ZSM-5 above 10 kpa butanol partial pressure (see Figure 3c). Such a profile has been reported by Zhi et al. for 1-propanol dehydration in H-ZSM-5 8. S44
For DBE formation (path B), the initial TOF for formation of DBE is essentially determined by the dimer mediated mechanism m 6. Accordingly, the initial (at conversion, X= 0) TOF for path B is given as: TOF at X= 0 = K K K k P 1+K P +K K P S.46 When (K K P 1+K P ), a positive order pressure dependence is possible and is seen in the low pressure regime for H-FAU and H-FER (P BuOH below 10 2 kpa) (see Figure 3c). Typically, DBE formation is favored at high pressure (K K P > >1+ K P ) and shows a zero order dependence with TOF = K k. A zero order dependence regime for path B is seen for H-ZSM-5 and H-ZSM-22 at butanol partial pressures below 1kPa and at moderate butanol partial pressures (between 1-50 kpa) for H- FER (see Figure 3c). A zero order is also reported for zeolite catalyzed conversion of methanol to dimethyl ether 9. For DBE decomposition (path C), the TOF for path C (TOF is obtained by summing up TOF contributions from each of the 2 mechanisms m 9 and m 10 and is given as: TOF = K k +K k P 1+ K P + K K P + K P S.47 Here K is the equilibrium coefficient for elementary step 22 (DBE* DBE2) and k and k are forward reaction rate coefficients for elementary steps 20 (m 9 via syn-elimination) and 23 (m 10 via anti-elimination), respectively. A simplified form of equation (S.22) is obtained under conditions when DBE* is MARI (i.e. 1+ K P + K K P < K P, see Figure S31 for H-ZSM-5 and H- ZSM-22 in a butanol partial pressure range of 10-2 to 1 kpa). Under these conditions a zero order dependence is seen with TOF = k +K k, which is observed in Figure 3c S45
for H-ZSM-5 and H-ZSM-22. A more complex dependence on 1-butanol partial pressure is seen (see Figure 3c), when DBE is not MARI (see Figure S30 for surface coverages). When the TOFs of DBE formation and DBE decomposition are comparable (see Figure 3c, TOFs of path B and C for H-FER), the TOF for DBE decomposition shows the same pressure dependence as that of DBE formation path. At high butanol partial pressures (above 50 kpa), when K P + K K P 1+ K P ), a negative order dependence on 1-butanol partial pressure is seen. S46
S10. References: (1) Cramer, C. J. Essentials of computational chemistry : theories and models; 2nd ed.; Wiley: Chichester Hoboken, NJ, 2004. (2) NIST Chemistry WebBook, NIST Standard Reference Database Number 69; National Institute of Standards and Technology, 2005. (3) Makarova, M. A.; Paukshtis, E. A.; Thomas, J. M.; Williams, C.; Zamaraev, K. I. J Catal 1994, 149, 36-51. (4) John, M.; Alexopoulos, K.; Reyniers, M. F.; Marin, G. B. J Catal 2015, 330, 28-45. (5) De Moor, B. A.; Reyniers, M. F.; Marin, G. B. Phys Chem Chem Phys 2009, 11, 2939-2958. (6) Chiang, H.; Bhan, A. J Catal 2010, 271, 251-261. (7) Macht, J.; Janik, M. J.; Neurock, M.; Iglesia, E. J Am Chem Soc 2008, 130, 10369-10379. (8) Zhi, Y.; Shi, H.; Mu, L.; Liu, Y.; Mei, D.; Camaioni, D. M.; Lercher, J. A. J Am Chem Soc 2015, 137, 15781 15794. (9) Jones, A. J.; Iglesia, E. Angew Chem Int Edit 2014, 53, 12177-12181. S47