Direct oxidation of methane to methanol using copper phthalocyanines as precursors;
: Gallego-Villada, Luis A.; Pätsch, Sebastian; Mäki-Arvela, Päivi; Efimov, Alexander; Doronkin, Dmitry E.; Mazur, Michal; Lastusaari, Mika; Elvers, Benedict J.; Virtanen, Pasi; Kumar, Narendra; Tirri, Teija; Schulzke, Carola; Murzin, Dmitry Yu.
Publisher: Elsevier BV
: 2026
Applied Catalysis B: Environmental
: 126987
: 398
: 0926-3373
: 1873-3883
DOI: https://doi.org/10.1016/j.apcatb.2026.126987
: https://doi.org/10.1016/j.apcatb.2026.126987
: https://research.utu.fi/converis/portal/detail/Publication/523750042
The direct oxidation of methane to methanol (DOMTM) in the liquid phase was investigated using a copper α-3,5-(di-tert-butyl)phenyl phthalocyanine (CuPc) supported on hierarchical ZSM-5 zeolites prepared by alkaline desilication, with H2O2 as an oxidant (50 ºC, 30 bar CH4, 0.5 M H2O2). Catalysts with varying Cu loadings (0.5–1.0 wt%), framework compositions (SiO2/Al2O3 = 23 and 30), and thermal treatment (intact CuPc vs. calcined) were evaluated. Qualitative kinetic analysis was performed through the quantification of the products over time (0–4 h) by HPLC, 1H NMR, and potentiometric titration. X-ray absorption spectroscopy (XAS) established that the CuPc macrocycle remains structurally intact after incorporation into the zeolite (Cu-N distance 1.94 Å, coordination number∼4.4), while calcination leads to complete macrocycle decomposition and formation of isolated Cu2+-2Z framework species, as confirmed by XANES, UV-Vis-diffuse reflectance spectroscopy, and H2-TPR. Elemental mapping by HAADF-STEM demonstrated that copper is homogeneously dispersed throughout the zeolite. Calcination significantly improved catalytic performance. The catalyst 1CuPc-ZSM-5–30-DS-Calc (Cu/Al molar ratio = 0.17) achieved a CH3OH productivity of 553 μmol gcat−1 h−1 and 47% selectivity at isoconversion (0.1%), corresponding to a methanol yield of 4.3 molCH3OH molCu−1 h−1, surpassing many recent reported phthalocyanine-based systems for DOMTM. An even higher methanol yield of 8.0 molCH3OH molCu−1 h−1 was obtained over 0.5CuPc-ZSM-5–30-DS-Calc (Cu/Al molar ratio = 0.09). The Brønsted to Lewis acid site (BAS/LAS) ratio and Brønsted acid site density were identified as key descriptors of CH3OH selectivity and productivity. These findings establish that CuPc functions primarily as a precursor to well-dispersed Cu²⁺ active sites, and that copper speciation, zeolite acidity, and mesoporosity jointly govern methanol selectivity in this reaction system.
BAS/LAS ratio, Copper phthalocyanine, Hierarchical ZSM-5, Isolated Cu2+ species, Methane oxidation, Methanol
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The authors acknowledge the Research Council of Finland for funding through the project “Methane to methanol by biomimetic catalysts” (Project No. 361444). The authors also thank the Institute of Biomedicine, University of Turku, which receives financial support from Biocenter Finland, for the analysis of samples by transmission electron microscopy (TEM). Financial support from PREIN Flagship program by the Research Council of Finland and Tampere University is gratefully acknowledged. The authors acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Parts of this research were carried out at PETRA III. Data was collected using P64 operated by DESY Photon Science. The authors thank Dr. Aleksandr Kalinko for his assistance with beamline setup. Beamtime was allocated under proposal I-20250078. Michal Mazur acknowledges the Ministry of Education, Youth and Sports of the Czech Republic for the ERDF/ESF grant TECHSCALE No. CZ.02.01.01/00/22_008/0004587 and the Charles University Centre of Advanced Materials (CUCAM—OP VVV Excellent Research Teams, no. CZ.02.1.01/0.0/0.0/15_003/0000417) for providing the TEM facility.
