摘要
用傅里哀变换红外(FT-IR)光谱原位考察了稀土氧化钐上甲烷氧化偶联反应及乙烯,乙烷的氧化反应。在700℃以下,甲烷,乙烯和乙烷分别与氧化钐表面反应时,除检测到表面碳酸基外,未观察到其它表面物种。这些表面碳酸基物种只有在700℃以上才大部分脱附,在氧存在下,高于700℃时这些低碳烃的完全氧化很显著,但在内循环反应体系中发现过量的气相CO_2可抑制烃类的深度氧化。甲烷的偶联反应在700℃以上才可明显观察到。而大部分表面碳酸基也在700℃以上才脱附,但经脱碳酸基或高温氧化处理后的氧化钐上均未明显观察到O^-物种的ESR峰。本文认为经高温脱碳酸基后形成的表面配位不饱和氧物种O^(δ-)(1<δ<2)在甲烷氧化偶联反应中起主要作用。
Methane oxidative coupling and oxidations of ethylene and ethane over Sm_2O_3 were studied by in situ Fourier-Transform Infrared (FT-IR) spectroscopy at the temperature range of 100-750℃. Surface carbonate species can be always detected when methane, ethylene and ethane react with Sm_2O_3 at temperatures above 400℃, but most of the carbonate species decompose and desorb at temperatures above 700℃, where the methane oxidative coupling to ethylene and ethane is initiated. With the presence of gaseous O_2, complete oxidation of these hydrocarbons becomes more prominent. However, additional surface species was not clearly observed at temperatures either under or above 700℃. It was found that an excess of CO_2 seems to depress the complete oxidation of methane. Dehydrogenation of ethane over Sm_2O_3 is very facile at temperature above 700℃ both in the presence and absence of O_2. Therefore the ethylene have been produced mainly via the dehydrogenation of ethane in the methane oxidative coupling reaction. No ESR signal due to oxygen intermediates such as O_2^- and O^- was observed for Sm_2O^3 at room temperature. It is suggested that the surface coordinatively unsaturated oxygen ion, O^(δ-)(1<δ<2) which was created through the decomposition of surface carbonate species is the effective species in the methane oxidative coupling process.
出处
《燃料化学学报》
EI
CAS
CSCD
北大核心
1992年第1期26-31,共6页
Journal of Fuel Chemistry and Technology
基金
国家自然科学基金
青年科学基金
关键词
甲烷
氧化偶联
烃类
氧化
氧化钐
methane oxidative coupling
oxidation of hydrocarbon
Sm_2O_3
FT-IR
