MOFs-derived N-doped carbon matrix superacid-catalyzed hydrocracking of a residue from thermal dissolution of Hefeng subbituminous coal

Abstract

An active, low-cost, and recyclable catalyst was prepared by impregnating trifluoromethanesulfonic acid (TFMSA) onto metal-organic frameworks (MOFs)-derived N-doped carbon matrix nanoparticles. The residue (RTD) from thermal dissolution (TD) of Hefeng subbituminous coal in methanol was subjected to further TD and catalytic hydrocracking (CHC) over the catalyst, i.e., TFMSA/MOFs at 300 °C in cyclohexane. Detailed molecular compositions of the soluble portions from TD (SPTD) and CHC (SPCHC) were characterized with a Fourier transform infrared spectrometer, gas chromatograph/mass spectrometer (GC/MS), and positive-ion atmospheric pressure chemical ionization orbitrap mass spectrometer (PIAPCIORMS). The results show that 15.60% of organic matter in RTD was converted to a soluble portion by the CHC, whereas the yield of SPTD is only 1.04%. According to the analysis with GC/MS, SPCHC is rich in alkyl-substituted benzenes, while most of the GC/MS-detectable compounds in SPTD are alkyl-substituted arenols, alkyl-substituted cyclenones, and phenylalkanones in addition to alkyl-substituted benzenes. The analysis with PIAPCIORMS shows that both the number and yields of basic nitrogen-containing species were dramatically reduced after the CHC. These facts indicate that TFMSA/MOFs effectively catalyzed the cleavage of Car–Calk bridged bonds connecting some aromatic rings (ARs) and side chains on some ARs in RTD to obtain soluble compounds. Di(1-naphthyl)methane and 2-(benzyloxy)naphthalene were used as coal-related model compounds (CRMCs) and their CHCs were investigated to further explore the catalysis of TFMSA/MOFs in the CHC of RTD. As a result, TFMSA/MOFs effectively catalyzed the cleavage of Car-Calk and C-O bonds in the CRMCs under moderate conditions. TFMSA/MOFs can be easily separated by using an external magnetic field and the recovered TFMSA/MOFs is still highly active for the CHC of DNM.