Catalysis Letters Supporting Information
Supporting Information: Effect of Impurities on the Initiation of the MTO Process:
Kinetic Modeling based on Ab Initio Rate Constants
Jonas Amsler · Philipp N. Plessow · Felix Studt
Contents
S1 Dehydration of EtOH . . . . 1
S2 Equilibration . . . . 2
S3 Kinetics with pure DME feed . . . . 2
S4 Kinetics with pure MeOH feed . . . . 2
S5 Kinetic Model . . . . 2
S6 Ab initio Reaction Barriers for the Kinetic Model . . . . 3
S1 Dehydration of EtOH
Dehydration of higher alkanols to olefins is viable in zeolites. [1] The simplest example is ethanol which dehydrates to ethene.
To consider the effect of EtOH impurities in this study, we extended the kinetic model by calculating the dehydration of EtOH via two steps:
ZOH+EtOH→ZOEt+H2O ∆G‡=183 kJ mol−1 (S1)
ZOEt→ZOH+C2H4 ∆G‡=163 kJ mol−1 (S2)
Using the previously employed MP2:DFT procedure, [2] the free energy barriers were computed to 183 kJ mol−1 and 163 kJ mol−1 for the forward reaction at a temperature of 673.15 K (see Fig. S1). The mechanism comprises the intermedi- ate ZOEt, the so-called surface ethyl species (SES) which has also recently been observed in NMR spectra of the ethanol-to- hydrocarbons (ETH) reaction with EtOH feed over H-ZSM-5 zeolite. [3] The individual energy contributions to the final free
ZOH ZOEt ZOH
H2O
ZOH EtOH
EtOH*
C2H4
Fig. S1 Calculated free energy diagram for the two-step dehydration of EtOH to ethene with the intermediate SES (ZOEt) in H-SSZ-13 at a temperature of 673.15 K and 1 bar EtOH as obtained from MP2:DFT and using the harmonic approximation. ZOH indicates the free acid site.
energy defined by equation (S3) are listed in Table S1.
Gfinal=EPBC(PBE-D3/400eV) +E46T(MP2/def2-TZVPP)−E46T(PBE-D3/def2-TZVPP) +∆G(trans,rot,vib) (S3)
Jonas Amsler·Philipp N. Plessow·Felix Studt
Karlsruhe Institute of Technology (KIT), Institute of Catalysis Research and Technology, Hermann-von-Helmholtz-Platz 1 76344 Eggenstein- Leopoldshafen
E-mail: philipp.plessow@kit.edu Felix Studt
Karlsruhe Institute of Technology (KIT), Institute for Chemical Technology and Polymer Chemistry, Kaiserstraße 12, 76131 Karlsruhe
Table S1 Contributions to the final free energy in eV at 673.15 K and a reference pressure of 1 bar.
species PBE-D3/400eV MP2/def2-TZVPP (T46) PBE-D3/def2-TZVPP (T46) ∆G(trans,rot,vib) Gfinal
EtOH -46.933 -4210.912 -4215.328 0.202 -42.315
H2O -14.224 -2076.857 -2078.416 -0.714 -13.379
C2H4 -31.984 -2133.377 -2136.159 -0.174 -29.375
ZOH -862.600 -508608.904 -509092.874 0.326 -378.304
ZOH*EtOH -910.863 -512820.966 -513309.518 1.782 -420.528
TS: ZOH*EtOH→ZOEt + H2O -909.244 -512819.070 -513307.922 1.670 -418.722
ZOEt -895.578 -510743.248 -511230.029 1.395 -407.401
TS: ZOEt→ZOH + C2H4 -894.329 -510741.497 -511228.790 1.325 -405.712
S2 Equilibration
Prior to kinetic simulations, the DME feed was equilibrated to methanol, water and corresponding surface species (SMS and adsorbates). The equilibrium composition was computed from the rate constants by solving the equation system (S4) containing all reactions (i) with the boundary condition of maintaining stoichiometry.
kforward kbackward
=Πproducts Πreactants i
(S4) The composition of the equilibrated mixture at 673 K is depicted in Fig. S2.
a) b)
Fig. S2 Normalized composition of equilibrated DME feed as at 673 K for a) gas phase and b) surface species. Side reactions to other compounds than the listed ones are not considered in the equilibration.
S3 Kinetics with pure DME feed
Additional kinetic simulations were carried out with pure DME feed and impurities of formaldehyde, ethanol and propene.
Fig. S3 depicts the evolution of DME, MeOH, H2O and the total pressure of olefins analogously to Fig. 2. The qualitative results are comparable to the results of the equilibrated DME feed. Here the olefin formation is preceded by the equilibration between DME and MeOH during which the SMS is formed.
S4 Kinetics with pure MeOH feed
Additional kinetic simulations were carried out with pure MeOH feed and impurities of formaldehyde, ethanol and propene.
Fig. S4 depicts the evolution of DME, MeOH, H2O and the total pressure of olefins analogously to Fig. 2. In contrast to pure or equilibrated DME feeds, the MeOH feed leads to a higher water pressure upon equilibration to DME and SMS. Due to the inhibiting effect of water in our model, the initiation period is significantly prolonged. Nevertheless, also in this case the investigated impurities lead to an earlier production of olefins.
S5 Kinetic Model
In our simulation, the change in partial pressures∆pidue to the elementary reaction with raterjand stoichiometric coefficient vji (vji=−2,−1,0,1,2) is computed simply as:∆pi≈vji×rj×∆t Here,rj is computed according to the involved partial
b) 2 mbar FA
DME DME DME DME
a) No impurity c) 2 mbar EtOH d) 2 mbar propene
H2O H2O H2O H2O
MeOH MeOH MeOH
MeOH
olefins olefins
olefins
olefins
Fig. S3 Results of the kinetic batch reactor model: Partial pressure evolution of a pure DME feed with (a) no impurities, (b) 2 mbar of formaldehyde, (c) 2 mbar of ethanol and (d) 2 mbar of propene. The black line shows shows the total partial pressure of the produced olefins. Two light off criteria for the olefin production are highlighted: the time after which the produced olefins surpass 1 mbar and their total partial pressure after 3 s.
b) 2 mbar FA
DME DME
DME
DME
a) No impurity c) 2 mbar EtOH d) 2 mbar propene
H2O H2O
H2O
H2O
MeOH MeOH MeOH
MeOH
olefins olefins
olefins olefins
Fig. S4 Results of the kinetic batch reactor model: Partial pressure evolution of a pure MeOH feed with (a) no impurities, (b) 2 mbar of formaldehyde, (c) 2 mbar of ethanol and (d) 2 mbar of propene. The black line shows shows the total partial pressure of the produced olefins. Two light off criteria for the olefin production are highlighted: the time after which the produced olefins surpass 1 mbar and their total partial pressure after 3 s.
pressures, coverages and rate constantskj. The total change in partial pressures is obtained by summing over all elementary processes. Finally,∆tis the time step, which needs to be chosen sufficiently small. We choose 10−10s for the first 1000 to 10 000 steps and 5·10−8s afterwards. Additionally, time steps are dynamically throttled so that any individual partial pressure decreases at most by 5 %. This rather simple and time-consuming way of solving the kinetics was adopted because it allows rigorous error control over the formation of autocatalytic impurities as opposed to more sophisticated and efficient algorithms of integrating the kinetics. Further details on the kinetic model can be found in the SI of our previous publication. [4]
S6 Ab initio Reaction Barriers for the Kinetic Model
Most reaction free energy barriers listed in Table S2 have been taken from literature. [2, 5] The barriers for the dehydration of ethanol have been discussed in Section S1 and in the methods section of the main text.
Table S2: Collection of all elementary reaction steps pertaining to the MTO initiation and olefin cycle. Free energy barriers in H-SSZ-13 are listed for forward and backward reaction. Highlighted in gray are potential impurities and co-feeds investigated in this work. Colors indicate the relation to the mechanism in Fig. 1 of the main text. The reaction free energies for the ethanol dehydration to ethene (steps no. 43 and 44) have been calculated in this work, all other reaction free barriers, as well as the nomenclature, have been taken from the literature, see references [2, 5, 6].
No. Elementary reaction ∆G‡ molkJ
Ref.
1 ZOH + H2O ZOH*H2O 109, 80 [2]
2 ZOH + MeOH ZOH*MeOH 82, 80 [2]
No. Elementary reaction ∆G‡ molkJ Ref.
3 ZOH*MeOH ZOMe + H2O 169, 177 [2]
4 ZOH + DME ZOH*DME 80, 81 [2]
5 ZOMe + MeOH ZOH*DME 151, 160 [2]
6 ZOH*MeOH + MeOH ZOH*DME + H2O 192, 210 [2]
7 ZOH*DME ZOCOMe + H2 220, 153 [2]
8 ZOMe + DME ZOCOMe + CH4 232, 296 [2]
9 ZOH*DME + DME ZOCOMe + CH4+ MeOH 245, 299 [2]
10 ZOH*MeOH + DME ZOCOMe + CH4+ H2O 260, 332 [2]
11 ZOH*MeOH ZOH + H2+ FA 226, 206 [2]
12 ZOH*MeOH + DME ZOH*MeOH + CH4+ FA 228, 328 [2]
13 ZOH*MeOH + MeOH ZOH*H2O + CH4+ FA 275, 361 [2]
14 ZOMe + MeOH ZOH + CH4+ FA 237, 345 [2]
15 ZOH + FA ZOH + CO + H2 251, 322 [2]
16 ZOMe + FA ZOCOMe 173, 137 [2]
17 ZOH*DME + FA ZOH + s ch4-fa 274, 456 [2]
18 ZOCOMe + DME ZOH + s ch4-fa 244, 456 [2]
19 ZOCOMe + MeOH ZOH + DMM 119, 121 [2]
20 ZOMe + DMM ZOMe + CH4+ MF 205, 394 [2]
21 ZOH*DME + DMM ZOMe + CH4+ MF + MeOH 235, 414 [2]
22 ZOH*MeOH + DMM ZOMe + CH4+ MF + H2O 255, 452 [2]
23 ZOH + DMM ZOMe + hacetal 145, 137 [2]
24 ZOH + hacetal ZOH + H2+ MF 181, 249 [2]
25 ZOH*DME + hacetal ZOH*MeOH + CH4+ MF 208, 394 [2]
26 ZOH*MeOH + hacetal ZOH*H2O + CH4+ MF 248, 423 [2]
27 ZOMe + hacetal ZOH + CH4+ MF 215, 412 [2]
28 ZOH + MF ZOH*MeOH + CO 135, 178 [2]
29 ZOMe+ CO ZO2CMe 190, 177 [2]
30 ZO2CMe ZOH+Ketene 80, 81 [2]
31 ZOMe+Ketene ZO2CEt 159, 203 [2]
32 ZO2CEt ZOH+Mketene 80, 82 [2]
33 ZOMe+Mketene ZO2CiPr 139, 192 [2]
34 ZO2CiPr ZOH+Dketene 80, 82 [2]
35 ZOMe +Dketene ZO2CtBu 136, 117 [2]
36 ZO2CMe+MeOH ZOH+ MA 97, 150 [2]
37 ZO2CEt+MeOH ZOH+MeO2CEt 81, 134 [2]
38 ZO2CiPr+MeOH ZOH+MeO2CiPr 83, 132 [2]
39 ZO2CtBu+MeOH ZOH+MeO2CtBu 83, 203 [2]
40 ZO2CEt ZOH+ CO + ethene 172, 239 [2]
41 ZO2CiPr ZOH+ CO + propene 130, 215 [2]
42 ZO2CtBu ZOH+ CO +C4b 10, 179 [2]
43 ZOH+ EtOH ZOEt+H2O 183, 199 this work
44 ZOEt ZOH+ ethene 163, 190 this work 45 ZOMe+ ethene ZOH+ propene 176, 250 [5]
46 ZOMe+ propene ZOH+C4a 155, 218 [5]
47 ZOMe+C4a ZOH+C5a 154, 218 [5]
48 ZOMe+C4a ZOH+C5b 171, 223 [5]
49 ZOMe+C4b ZOH+C5a 147, 206 [5]
50 ZOMe+C5a ZOH+C6a 132, 196 [5]
51 ZOMe+C5b ZOH+C6b 159, 209 [5]
52 ZOMe+C5b ZOH+C6c 149, 213 [5]
53 ZOMe+C6a ZOH+C7a 146, 188 [5]
54 ZOMe+C6a ZOH+C7b 130, 162 [5]
55 ZOMe+C6b ZOH+C7c 146, 200 [5]
56 ZOMe+C6b ZOH+C7d 141, 202 [5]
57 ZOMe+C7a ZOH+C8a 115, 169 [5]
58 ZOMe+C7b ZOH+C8b 110, 168 [5]
59 ZOMe+C7c ZOH+C8c 174, 222 [5]
No. Elementary reaction ∆G‡ molkJ Ref.
60 ZOMe+C7c ZOH+C8d 154, 214 [5]
61 ZOMe+C8a ZOH+C9a 130, 156 [5]
62 ZOMe+C8b ZOH+C9a 129, 160 [5]
63 ZOMe+C8c ZOH+C9b 171, 220 [5]
64 ZOMe+C8c ZOH+C9c 142, 208 [5]
65 ZOH*MeOH+ ethene ZOH*H2O+ propene 208, 260 [5]
66 ZOH*MeOH+ propeneZOH*H2O+C4a 195, 236 [5]
67 ZOH*MeOH+C4a ZOH*H2O+C5a 178, 221 [5]
68 ZOH*MeOH+C4b ZOH*H2O+C5b 200, 232 [5]
69 ZOH*MeOH+C5a ZOH*H2O+C6a 157, 199 [5]
70 ZOH*MeOH+C5b ZOH*H2O+C6b 187, 216 [5]
71 ZOH*MeOH+C5b ZOH*H2O+C6c 176, 219 [5]
72 ZOH*MeOH+C6a ZOH*H2O+C7b 140, 151 [5]
73 ZOH*MeOH+C6b ZOH*H2O+C7c 194, 227 [5]
74 ZOH*MeOH+C6b ZOH*H2O+C7d 173, 213 [5]
75 ZOH*MeOH+C7b ZOH*H2O+C8b 156, 193 [5]
76 ZOH*MeOH+C7c ZOH*H2O+C8c 201, 229 [5]
77 ZOH*MeOH+C7c ZOH*H2O+C8d 198, 238 [5]
78 ZOH*DME+ ethene ZOH*MeOH+ propene 216, 276 [5]
79 ZOH*DME+ propene ZOH*MeOH+C4a 208, 258 [5]
80 ZOH*DME+C4a ZOH*MeOH+C5a 195, 247 [5]
81 ZOH*DME+C4a ZOH*MeOH+C5b 207, 247 [5]
82 ZOH*DME+C5a ZOH*MeOH+C6a 165, 215 [5]
83 ZOH*DME+C5b ZOH*MeOH+C6b 208, 245 [5]
84 ZOH*DME+C5b ZOH*MeOH+C6c 183, 234 [5]
85 ZOH*DME+C6a ZOH*MeOH+C7b 173, 192 [5]
86 ZOH*DME+C6b ZOH*MeOH+C7c 194, 235 [5]
87 ZOH*DME+C6b ZOH*MeOH+C7d 190, 238 [5]
88 ZOH*DME+C7b ZOH*MeOH+C8b 165, 210 [5]
89 ZOH*DME+C7c ZOH*MeOH+C8d 187, 234 [5]
90 ZOH+C4a ZOH+ 2 ethene 246, 210 [5]
91 ZOH+C5a ZOH+ ethene + propene 211, 185 [5]
92 ZOH+C5b ZOH+ ethene + propene 238, 224 [5]
93 ZOH+C6b ZOH+ ethene +C4a 211, 209 [5]
94 ZOH+C6c ZOH+ ethene +C4b 186, 177 [5]
95 ZOH+C6c ZOH+ 2 propene 199, 194 [5]
96 ZOH+C7a ZOH+ propene +C4a 187, 191 [5]
97 ZOH+C7a ZOH+ ethene +C5a 179, 174 [5]
98 ZOH+C7b ZOH+ propene +C4a 209, 220 [5]
99 ZOH+C7c ZOH+ propene +C4a 215, 233 [5]
100 ZOH+C7d ZOH+ ethene +C5a 168, 169 [5]
101 ZOH+C8a ZOH+ propene +C5a 168, 183 [5]
102 ZOH+C8b ZOH+C4a+C4b 111, 135 [5]
103 ZOH+C8c ZOH+ propene +C5b 200, 221 [5]
104 ZOH+C8d ZOH+ propene +C5b 236, 245 [5]
105 ZOH+C9a ZOH+C4b+C5a 87, 145 [5]
106 ZOH+C9b ZOH+ propene +C6b 201, 224 [5]
107 ZOH+C9c ZOH+ propene +C6b 233, 238 [5]
References
1. Feˇc´ık M, Plessow PN, Studt F (2018) J Phys Chem C 122:23062 2. Plessow PN, Studt F (2017) ACS Catal 7:7987
3. Chowdhury AD, Lucini Paioni A, Whiting GT, Fu D, Baldus M, Weckhuysen BM (2019) Angew Chem Int Ed 58:3908 4. Plessow PN, Smith A, Tischer S, Studt F (2019) J Am Chem Soc 141:5908
5. Plessow PN, Studt F (2018) Catal Sci & Technol 8:4420 6. Plessow PN, Studt F (2020) Catal Sci & Technol 10:6738
