Pyrolysis Behaviors Of Coal-Related Model Compounds Catalyzed By Ni Or Co-modified HZSM-5 Zeolite

Coal is a reliable and abundant fossil resource.Because both the structure of coal and the pyrolysis process of coal are complex from the perspective of chemistry,it is of theoretical significance to choose coal-related model compounds to explore the catalytic pyrolysis process.HZSM-5 is an excellent catalyst carrier,which can extract high quality light pyrolysis oils from coal under mild conditions.In this paper,a series of nickel-based and cobalt-based catalysts were prepared using HZSM-5 as carriers by the impregnation method.The structural properties of the catalyst samples were investigated using characterization techniques such as Powder X-ray diffraction（XRD）,fourier transform infrared spectroscopy（FT-IR）,ultraviolet and visible spectrophotometry（UV-Vis）,temperature-programmed reduction（H₂-TPR）and temperature-programmed desorption（NH₃-TPD）.The catalytic effects and mechanisms of these catalysts in the pyrolysis of the coal-related model compounds（phenyl ethyl ether,benzyloxybenzene,bibenzyl）were explored on a fixed-bed pyrolysis reactor,and the influence of different types and valence of the metals on the catalytic performance were also discussed.This provides a basis for understanding the catalytic reaction patterns of coal at the molecular level.The main findings are as follows:（1）Ni O has an obvious dehydrogenation effect.Under the appropriate nickel loading,Ni O/HZSM-5 can effectively promote the non-radical reaction of phenyl ethyl ether to produce more phenolic compounds.The Ni O species on HZSM-5 is more superior to the Ni species in the pyrolysis of phenyl ethyl ether.During the catalytic pyrolysis of benzyloxybenzene,Ni O/HZ-1 whose metal loading is 1.26 wt.%can effectively promote the cleavage of the C_aliphatic-O bond of benzyloxybenzene.While in the catalytic pyrolysis of bibenzyl,the catalytic effect of multiple catalysts are poor.（2）During the pyrolysis of phenyl ethyl ether,the dealkylation effect of Co₃O₄ is very significant.Co₃O₄/HZSM-5 with the appropriate cobalt loading can promote the cleavage of the C_aliphatic-O bond of phenyl ethyl ether to form phenoxy,which can further combine with H-to form a large amount of phenol.Co₃O₄/HZ-2 whose metal loading is 2.02 wt.%can reduce the yield of char in the pyrolysis of benzyloxybenzene and increase the oil to gas ratio of the product.The pyrolysis conversion of bibenzyl catalyzed by Co₃O₄/HZSM-5 decreased with increasing cobalt loading,and the catalytic effect are poor.