Design of alkali salt supported gasification catalyst and combustion of particulate in the exhaust gas from diesel engine

研究了在673~773K温度范围内，碱金属碳酸盐在碳、Almina和钙钛矿型氧化物(La_&lt；0.8&gt；SR_&lt；0.2&gt；Cr_&lt；0.5&gt；Mn_&lt；0.45&gt；PT_&lt；0.05&gt；O_3，LSCMP)上的催化活性。并对典型的过渡金属氧化物催化剂V_2O_5/γ-Al_2O_3的催化活性进行了比较。碳负载碳酸钾在723K时表现出最大的燃烧初始速率，而3h内的转化率几乎与碱金属/碳的比例成正比。V_2O_5γ-Al_2O_3的转化率也随催化剂用量的增加而线性增加，但斜率较小，表明催化剂的转化率有限。相比之下，在碱金属/碳比低至0.012的条件下，负载碳酸盐的催化剂表现出较高的转化率，表明其具有很大的催化转化率，而初始活性与碳上相同盐类的活性相当。然而，γ-Al_2O_3和LSCMP单独负载的碳酸盐的活性非常有限。在673K时，LSCMP负载的碳酸盐的活性高于碳负载的碳酸盐。LSCMP上的碱式碳酸盐似乎在较低的温度下表现出活性。还测定了其他碱性碳酸盐的活性，以考察LSCMP载体的作用。从催化燃烧中碱金属盐的还原活化、载体上活性物种的升华、捕集和逸出等角度对实验结果进行了讨论。推导了LSCMP的独特作用。

Catalytic activity of alkali metal carbonates was studied for the combustion of activated carbon grains at 673-773 K by supporting the carbonates on carbon, almina, and a perovskite-type oxide (La_<0.8> Sr_<0.2> Cr_<0.5> Mn_<0.45> Pt_<0.05> O_3, LSCMP). Catalytic activity of V_2O_5/γ -Al_2O_3 as a typical transition metal oxide catalyst was also measured for comparison. Potassium carbonate supported on the carbon exhibited the largest initial rate of the combustion among the catalysts at 723 K, while the achieved conversion within 3h increased almost proportional to the ratio of alkali metal to carbon. V_2O_5γ-Al_2O_3 also showed linear increase of achieved conversion with the amount of catalyst, although the slope was much smaller, indicating that the catalytic turnover number is limited. In contrast, the carbonate supported on LSCMP showed high conversion at an alkali metal to carbon ratio as low as 0.012, indicating a very large catalytic turnover number while the initial activity was comparable to that of the same salts on carbon. However, the carbonate supported on γ-Al_2O_3 and LSCMP alone showed very limited activity. The carbonate supported on LSCMP showed higher activity than carbonates supported on carbon at 673 K. The alkali carbonate seems to be active at lower temperatures on LSCMP. The activities of other alkali carbonates were also measured to examine the role of LSCMP support. Results are discussed from the view point of the reductive activation of the alkali metal salts, sublimation, trapping, and escape of the active species on the support in the catalytic combustion. The unique roles of LSCMP are deduced.