ABSTRACT

Rare earth elements and their compounds can be used as catalysts or promoters for pyrolysis of organic matter including those in coal, but relevant investigations, especially regarding the role of rare earth materials in coal pyrolysis are very scarce. This study focuses on the effect of cerium oxide (CeO₂) and lanthanum oxide (La₂O₃) on the formation of gaseous products from low-rank coal pyrolysis by means of gas chromatography (GC). The mechanisms of two kinds of rare earth oxides (REOs) involved in the coal pyrolysis are also discussed tentatively. Results show that CeO₂ can promote the formation of CO₂ (400°C–600°C), CO (550°C–650°C), CH₄ (300°C–500°C), C₂H₆ and C₃H₈ (350°C–750°C), and it is believed to catalyze the bond breaking reactions of the aliphatic side chain, carboxyl group and phenolic hydroxyl group, or the bridge bonds between aromatic nuclei. The catalytic effect of CeO₂ on the breaking of bridge bonds is likely to be completed by the movement of oxygen vacancies (i.e., oxygen storage and release ability of CeO₂) in the water vapor environment. In addition, the results also reveal that it is La₂O(CO₃)₂, not La₂O₃, playing a role in coal pyrolysis, which can promote the formation of CO₂ (500°C–750°C), H₂ and unsaturated hydrocarbons (350°C–500°C), and could be considered to be a catalyst for dehydrogenation at low-medium temperature. The mechanism of CO₂ formation catalyzed by La₂O(CO₃)₂ is probably related to the decomposition of oxygen-containing ligands formed by La(III) and carboxyl group at high temperature.

摘要

稀土元素及其化合物可用作煤中有机物热解的催化剂或促进剂，但相关研究，特别是稀土材料在煤热解中的作用研究甚少。本研究通过气相色谱法 (GC)重点研究氧化铈 (CeO ₂ ) 和氧化镧 (La ₂ O ₃ ) 对低阶煤热解气态产物形成的影响。还初步讨论了两种稀土氧化物（REOs）参与煤热解的机制。结果表明，CeO ₂可以促进CO ₂ (400°C–600°C)、CO (550°C–650°C)、CH ₄ (300°C–500°C)、C _{2 的形成}H ₆和 C ₃ H ₈ (350°C–750°C)，据信催化脂肪族侧链、羧基和酚羟基的键断裂反应，或芳香核之间的桥键。CeO ₂对桥键断裂的催化作用很可能是通过氧空位的运动（即CeO _{2 的}氧储存和释放能力）在水蒸气环境中完成的。此外，结果还表明，在煤热解中起作用的是La ₂ O(CO ₃ ) ₂，而不是La ₂ O ₃，可以促进CO ₂的形成。(500°C–750°C)、H ₂和不饱和烃(350°C–500°C)，可被认为是中低温脱氢的催化剂。La ₂ O(CO ₃ ) ₂催化CO ₂形成的机理可能与La(III)和羧基形成的含氧配体在高温下分解有关。