Improving aromatic hydrocarbons yield from coal pyrolysis volatile products over HZSM-5 and Mo-modified HZSM-5

•A novel application of Mo/HZSM-5 on improving BTEXN yield was investigated in situ.•The yield of BTEXN from coal pyrolysis was increased remarkably by HZSM-5 and Mo/HZSM-5.•The conditions and principle of Mo/HZSM-5 improving BTEXN yield were obtained. The effect of Mo/HZSM-5 and HZSM-5 on the yield of aromatic hydrocarbons such as BTEXN (benzene, toluene, ethylbenzene, xylene, naphthalene) during Pingshuo Coal flash pyrolysis at different temperatures was analyzed using Py-GC/MS. It shows that both HZSM-5 and Mo/HZSM-5 can remarkably increase the yield of BTEXN. HZSM-5 shows the highest catalytic activity at 900°C, the total BTEXN yield increases from 116ng/mg at 500°C to a maximum of 7000ng/mg at 900°C, and then decreases with further increase of temperature. The maximum yield with HZSM-5 obtained at 900°C is more than three times that without HZSM-5. However, Mo/HZSM-5 has the potential to yield more BTEXN, as the maximum yield of BTEXN is 7020ng/mg at 800°C. The results indicate that Mo has been loaded on the HZSM-5 zeolite as MoO3. As a result, Mo/HZSM-5 can promote the aromatization of olefins and alkanes, dehydroxylation of phenolic compounds, as well as aromatization of CH4. Thus, Mo/HZSM-5 is more suitable for the catalytic conversion of the gaseous products from coal pyrolysis into BTEXN.