ENHANCEMENT OF THE CATALYTIC ACTIVITY OF ACTIVATED CARBONS IN OXIDATION REACTIONS BY THERMAL-TREATMENT WITH AMMONIA OR HYDROGEN-CYANIDE AND OBSERVATION OF A SUPEROXIDE SPECIES AS A POSSIBLE INTERMEDIATE
ENHANCEMENT OF THE CATALYTIC ACTIVITY OF ACTIVATED CARBONS IN OXIDATION REACTIONS BY THERMAL-TREATMENT WITH AMMONIA OR HYDROGEN-CYANIDE AND OBSERVATION OF A SUPEROXIDE SPECIES AS A POSSIBLE INTERMEDIATE
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DOI：
10.1016/0008-6223(91)90006-5
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发表时间：
1991-01-01
期刊：
影响因子：
10.9
通讯作者：
SCHLOGL, R
中科院分区：
文献类型：
--
作者：
STOHR, B;BOEHM, HP;SCHLOGL, R
在高温（600 ~ 900℃）条件下，用NH3或HCN处理后，活性炭与O2氧化反应的催化活性增强。测定了稀水H2SO3的氧化反应，作为催化活性的测试。在处理过程中，氮被化学吸附，XPS显示两个N 1s信号，结合能分别为401 ~ 400ev和399 ~ 398 eV，分别分配给胺基和类腈氮和/或类吡啶氮。在HCN处理下，表面氮含量高于体内氮含量，可达微孔体积减小。将氮气加热到900摄氏度就可以重新打开。在H-2或N2中加热至900℃后，催化活性显著提高，但N含量明显降低。碳在900℃下与NH3反应部分气化，导致微孔范围内孔隙体积增大。用300 K吸附的H2O和80 K吸附的N2和O2进行热解吸实验，证明了nh3活性炭中存在分子尺度非常窄的微孔。O2在190 ~ 210 K处有一个可逆化学吸附O2的解吸峰，可测的解吸峰延伸至T ~ 300 K。当O2吸附在HOPG上时，也观察到该解吸峰。在T < 170 K时的XPS测量显示，在0 1s b.e.处有533 eV的信号，该信号被分配给O2-离子。nh3活性炭在T < 170 K时催化H-2和O2生成H2O。进一步的化学证据的存在的O2-描述。此外，还发现细粒径的合成石墨对H2SO3氧化也有催化作用。化学吸附的氮原子似乎增强了催化活性，但活性物质的浓度低于XPS检测的极限。
The catalytic activity of activated carbons in oxidation reactions with O2 is enhanced after treatment with NH3 or HCN at elevated temperatures (600-900-degrees-C). The oxidation of dilute aqueous H2SO3 was measured as a test of catalytic activity. Nitrogen is chemisorbed in the treatment and XPS showed two N 1s signals with binding energies of 401-400 eV and 399-398 eV which are assigned to amine groups and nitrile and/or pyridine-like nitrogen, respectively. In the case of HCN treatment, the N content was higher on the surface than in the bulk, and the accessible micropore volume was reduced. It could be reopened by heating in N2 to 900-degrees-C. The catalytic activity was significantly increased after heating in H-2 or N2 to 900-degrees-C although the N content was considerably reduced.The carbon is partly gasified in the reaction with NH3 at 900-degrees-C leading to an increase of the pore volume in the micropore range. Thermodesorption experiments with H2O, adsorbed at 300 K, and N2 and O2 adsorbed at ca. 80 K gave evidence of the presence of very narrow micropores of molecular dimensions in the NH3-activated carbon. With O2, a desorption peak for a reversibly chemisorbed O2 species was observed at 190-210 K with measurable desorption extending to T > 300 K. This desorption peak was also observed with O2 adsorbed on HOPG. XPS measurements at T < 170 K showed a signal at an O 1s b.e. of 533 eV which is assigned to O2- ions. The NH3-activated carbon catalyzed H2O formation from H-2 and O2 at T < 170 K. Further chemical evidence for the presence of O2- is described. In addition, it was found that also synthetic graphite of fine particle size catalyzed H2SO3 oxidation. The catalytic activity seems to be enhanced by chemisorbed nitrogen atoms, but the concentration of the active species is below the limits of XPS detection.