Supporting information for

Transcription

1 Supporting information for Methane Dehydroaromatization by Mo/HZSM-5: Mono- or Bifunctional Catalysis? Nikolay Kosinov*, Ferdy J.A.G. Coumans, Evgeny A. Uslamin, Alexandra S.G. Wijpkema, Brahim Mezari and Emiel J.M. Hensen * Schuit Institute of Catalysis, Laboratory of Inorganic Materials Chemistry, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands Corresponding authors: Nikolay Kosinov Eindhoven University of Technology PO Box 513, 5600 MB Eindhoven The Netherlands Tel: n.a.kosinov@tue.nl Emiel J.M. Hensen Eindhoven University of Technology PO Box 513, 5600 MB Eindhoven The Netherlands Tel: e.j.m.hensen@tue.nl 1

2 Table S1. Catalytic performance of analyzed mixtures of catalysts (conditions: WHSV 2 h -1, 700 C, 16 h). Total amount of Selectivity (%) Mixture Pretreatment converted methane (mmol/g cat) C 6H 6 Coke C 7H 8 C 8H 10 C 2H 4+C 2H 6 HZSM-5 SiC < SiC Mo/C+HZSM SiC Mo/Al 2O 3+HZSM SiC Mo/SiO 2+HZSM SiC Mo/HZSM-5+HZSM

3 Figure S1. Methane conversion versus time on stream for (a) Mo/Al 2 O 3 +HZSM-5, (b) Mo/C+HZSM-5; (c) Mo/SiO 2 +HZSM-5 and (d) Mo/HZSM-5+HZSM-5 series of catalyst mixtures. 3

4 Figure S2. Benzene yield versus time on stream for (a) Mo/Al 2 O 3 +HZSM-5, (b) Mo/C+HZSM-5; (c) Mo/SiO 2 +HZSM-5 and (d) Mo/HZSM-5+HZSM-5 series of catalyst mixtures. 4

5 Figure S3. DTG profiles of spent single catalysts: (red) Mo/SiO 2 and (green) Mo/HZSM-5. Conditions: 5 C/min, O 2 /He 33/67, 40 ml/min. Figure S4. DTG profiles of separated components of spent physical mixtures: (left) Mo/SiO 2 +HZSM-5 (He-0) and (right) Mo/HZSM-5+HZSM-5 (He-0). Conditions: 5 C/min, O 2 /He 33/67, 40 ml/min. In the DTG profiles two clear weight loss peaks can be seen: one at about 450 C (soft coke) and another at about 600 C (hard coke). Soft coke is known to be associated with Mo, while hard coke is associated with Brønsted acid sites [1]. The fact that some hard coke can be seen in Mo/SiO 2 component of the Mo/SiO 2 +HZSM-5 mixture (Fig. S5 left) suggests that some of HZSM-5 particles are crushed during filling/emptying the reactor and sieving, leading to contamination of the Mo-containing fraction (because there is no hard coke in case of Mo/SiO 2 +SiC Fig. S4). On the other hand the absence of any soft coke in TG profiles of pure HZSM-5 components evidences effective separation of pristine zeolite fractions. 5

6 Figure S5. Combustion TG profiles of Mo/C catalyst (black) and Mo/C catalyst pre-heated in flow of He till 950 C (main text Fig. 3). Conditions: 10 C/min, O 2 /He 33/67, 40 ml/min. These TG profiles demonstrate that upon heating in He there is actually no sublimation of MoO 3 from Mo/C catalyst (due to carbothermal reaction leading to formation of refractory Mo 2 C) as the amount of MoO 3 remaining on both samples (inset graph) is very similar. 6

7 Figure S6. DTG profile of Mo/C catalyst in flow of air. Conditions: 10 C/min, 40 ml/min He flow. The sublimation behavior of unsupported MoO 3 (the remaining after carbon combustion is unsupported MoO 3 ) is very similar to that of Mo/SiO 2 catalyst (main text Fig. 3), suggesting weak bonding of MoO x species to the silica surface. 7

8 Figure S7. Dependence of XRD crystallinity of HZSM-5 fraction in the Mo/SiO 2 +HZSM-5 mixture on the amount of Mo migrated to the HZSM-5 during thermal treatment in He flow. A good power correlation (y = bx n +100) between the XRD crystallinity and the Mo content of the zeolite fraction as well as n being 2.58 strongly indicate the involvement of several Mo atoms in the dealumination process. 8

9 Figure S8. Benzene yield vs time on stream obtained during MDA tests with 5%Mo/HZSM-5 catalysts, heated to 700 C directly in methane flow (CH 4 ) or in He flow and held under He for corresponding number of hours (He-1, He-3, He-6) before switched to methane. Conditions: 700 C, atmospheric pressure, 0.3 g of catalyst, CH 4 WHSV 2.0 h -1, no dilution with SiC. 9

10 Figure S9. Weight normalized IR spectra of adsorbed pyridine on HZSM-5 and HMOR based catalysts after evacuation at 350 C (left). Acidity of catalysts as determined by integration of IR spectra of adsorbed pyridine after evacuation at 350 C (right). The spectra show comparable number of acid sites for both HZSM-5 / HMOR and 5%Mo/HZSM-5 / 5%Mo/HMOR series of samples. This is a result of similar Si/Al ratio and Mo content of the prepared samples, i.e. similar loading of Mo leads to comparable number of Brønsted acid sites interacting with MoO x. In turn, there was nearly no adsorption of pyridine detected on silicalite-1, indicating absence of any significant Brønsted acidity in this aluminum-free zeolite. 10

11 Table S2. Surface atomic concentrations determined by XPS for Mo/HZSM-5 and Mo/Silicalite-1 series of catalysts Sample # Surface atomic concentration (%) O C Si Al Mo 0.25%Mo/HZSM-5 0.5%Mo/HZSM-5 1%Mo/HZSM-5 2%Mo/HZSM-5 5%Mo/HZSM %Mo/Silicalite-1 0.5%Mo/Silicalite-1 1%Mo/Silicalite-1 2%Mo/Silicalite-1 5%Mo/Silicalite

12 Figure S10. Benzene and coke selectivity as function of Mo loading for the series of HZSM-5 and Silcialite-1 supported catalysts. Conditions: 700 C, atmospheric pressure, 0.3 g of catalyst, CH 4 WHSV 2.0 h -1, no dilution with SiC. References [1] Tempelman, C.H.L.; Hensen, E.J.M. Appl. Catal., B. 2015, ,