New Insights into Alkali-Catalyzed Gasification Reactions of Carbon: Comparison of N2O Reduction with Carbon over Na and K Catalysts
New Insights into Alkali-Catalyzed Gasification Reactions of Carbon: Comparison of N2O Reduction with Carbon over Na and K Catalysts
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DOI：
10.1006/jcat.2000.2817
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发表时间：
2000-05
影响因子：
7.3
通讯作者：
Zhonghua Zhu;G. Lu;R. T. Yang
中科院分区：
文献类型：
--
作者：
Zhonghua Zhu;G. Lu;R. T. Yang
研究了在 Na 和 K 浸渍的活性炭（Na/AC 和 K/AC）上将 N2O 催化转化为 N2。 K和Na是C-NOx反应中两种代表性且最活跃的催化剂。通过 N2 吸附、热分解（使用 TGA）、TPD 和 250°C 下的 CO2 化学吸附对具有不同 K 和 Na 负载量的碳样品进行表征。事实证明，250°C 下的 CO2 化学吸附对于钾分散度的测量有效，但对于钠分散度的测量则无效。使用N2O作为反应物有助于观察和分析气碳反应的反应机理，因为它易于解离化学吸附，而且C-N2O反应是一个基元反应。基于等温反应和 TPR，发现钾在 N2O 解离和氧转移方面都更活跃，从而产生更高的活性。研究发现K/C是一种优良的N2O分解催化剂。在 150–250°C 的低温范围内，K/C 上产生大量 N2，而没有碳气化。仅在较高温度下才会产生大量二氧化碳。两种碱金属活性差异的根本原因是三个因素的综合作用。首先，K/C 对于 N2O 解离非常活跃。由此产生的O原子将形成活性表面中间体，很可能是环氧中间体，它显着削弱了气化的表面C-C键（这是Chen和Yang统一机制的基础）。其次，表面酚盐基团也削弱了C-C键以促进气化，但-C-O-K基团的削弱比-C-O-Na基团的削弱更明显。第三，K2O在碳上的分散性高于Na2O。
Catalytic conversion of N2O to N2 over Na- and K-impregnated activated carbon (Na/AC and K/AC) was investigated. K and Na are two representative and most active catalysts for the C–NOx reactions. Carbon samples with different K and Na loadings were characterized by N2 adsorption, thermal decomposition (with TGA), TPD, and CO2 chemisorption at 250°C. CO2 chemisorption at 250°C proved to be effective for the measurement of potassium dispersion but not for sodium. Using N2O as the reactant facilitated the observation and analysis of the reaction mechanism of gas–carbon reactions due to its readiness for dissociative chemisorption and also because the C–N2O reaction is an elementary reaction. Based on isothermal reactions and TPR, potassium was found to be more active in both N2O dissociation and oxygen transfer thus gave rise to a much higher activity. It was found that K/C was an excellent catalyst for N2O decomposition. In the low-temperature range of 150–250°C, a significant amount of N2 was produced on K/C with no carbon gasification. Significant CO2 production occurred only at higher temperatures. The fundamental reason for the difference in activities of the two alkali metals is a combination of three factors. First, K/C is highly active for N2O dissociation. The O atoms thus produced would form active surface intermediates, most likely the epoxy intermediate which significantly weakened the surface C–C bonds for gasification (which is the basis of the unified mechanism of Chen and Yang). Second, the surface phenolate group also weakened the C–C bond to facilitate gasification, but the weakening was more pronounced by the –C–O–K group than by the –C–O–Na group. Third, the dispersion of K2O on carbon was higher than that of Na2O.