The Effect Of Catalyst Valence Change On Benzoic Acid Pyrolysis Using DFT

Catalytic pyrolysis is one of the important methods for coal pyrolysis,and it is also the key link in the process of coal rank transformation.Suitable catalysts in coal pyrolysis not only reduce the reaction temperature and adjust the yield and composition of the product,but also improve the conversion rate of coal.Because the chemical structure of coal is very complex,the catalytic pyrolysis mechanisms in coal are very difficult to study at the molecular level.Therefore,model compound is used in the theoretical study due to the high complexity of coal.In our previous work,we explored the effects of ZnO,?-Al₂O₃,CaO and MgO which all are stable catalysts on C₆H₅COOH,C₆H₅OCH₃ and C₆H₅CHO by density functional theory?DFT?for the first time.However,in the actual coal pyrolysis,the catalyst,such as Co₃O₄,Fe₂O₃ and Ni O,will change the valence with the reaction temperature or reaction time increasing.The reduction behavior of the catalyst will affect the coal pyrolysis.Therefore,it is of great significance to design and develop the catalyst for coal catalytic pyrolysis by exploring the effect of catalyst valence change.In this paper,C₆H₅COOH is selected as coal based model compounds,Cobalt?Co₃O₄?CoO and Co?,Iron?Fe₂O₃?Fe₃O₄?FeO and Fe?and Nickel?NiO and Ni?as catalysts to study the effect of valence change of catalysts on the reaction of carboxyl removal in catalytic pyrolysis of coal by DFT method,The main conclusions are as follows:1.The pyrolysis process of C₆H₅COOH is C₆H₅COOH?CO₂+C₆H₆ and C₆H₅COOH?C₆H₆COO?CO₂+C₆H₆.2.Cobalt Catalysts,For C₆H₅COOH pyrolysis on Co₃O₄?110?-B,the preferred reaction pathway is C₆H₅COOH?g??*C₆H₅COO+*H?*C₆H₅+*CO₂+*H?*C₆H₆+*CO₂?CO₂?g?+C₆H₆?g?.On CoO?100?,the preferred reaction pathway is C₆H₅COOH?g??*C₆H₅COO+*H?*C₆H₆+*CO₂?CO₂?g?+C₆H₆?g?.On Co?111?,the preferred reaction pathway is C₆H₅COOH?g??*C₆H₅COOH?*C₆H₅COO+*H?*C₆H₆+*CO₂?CO₂?g?+C₆H₆?g?.It is found that the highest barrier energy order is:Ea?CoO?<Ea?Co₃O₄?<Ea?Co?.Co₃O₄ and CoO promoted the removal of carboxyl group,but Co didn't.3.Iron Catalysts,For C₆H₅COOH pyrolysis on?-Fe₂O₃?0001?,the preferred reaction pathway is C₆H₅COOH?g??*C₆H₅COO+*H?*C₆H₆+*CO₂?CO₂?g?+C₆H₆?g?.on Fe₃O₄?111?,the preferred reaction pathway is C₆H₅COOH?g??*C₆H₅COO+*H?*C₆H₅+*CO₂+*H?*C₆H₆+*CO₂?CO₂?g?+C₆H₆?g?.On FeO?100?,the preferred reaction pathway is C₆H₅COOH?g??*C₆H₅COO+*H?*C₆H₆+*CO₂?CO₂?g?+C₆H₆?g?.On Fe?100?,the preferred reaction pathway is C₆H₅COOH?g??*C₆H₅COOH?*C₆H₅COO+*H?*C₆H₆+*CO₂?CO₂?g?+C₆H₆?g?.It is found that the highest barrier energy order is:E_a?Fe₃O₄?<E_a?FeO?<E_a??-Fe₂O₃??E_a?Fe?.Fe₃O₄ and FeO can promote the catalytic pyrolysis to some extent.The catalytic effect of?-Fe₂O₃ and metal Fe are not obvious.4.Nickel Catalysts,For C₆H₅COOH pyrolysis on NiO?100?,the preferred reaction pathway is C₆H₅COOH?g??*C₆H₅COO+*H?*C₆H₆+*CO₂?CO₂?g?+C₆H₆?g?.On Ni?111?,the preferred reaction pathway is C₆H₅COOH?g??*C₆H₅COOH?*C₆H₅COO+*H?*C₆H₆+*CO₂?CO₂?g?+C₆H₆?g?.It is found that they are catalytic to the reaction of carboxyl group removal in coal pyrolysis,and their catalytic performances show the order:NiO>Ni.