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采用共浸渍法制备了系列Co基/分子筛催化剂,在固定床催化反应器中考察了不同催化剂在甲烷催化还原NO_x中的催化行为,优化了Co基/分子筛催化剂的助剂和载体,并通过催化表征手段阐明了其构效关系.结果表明,Fe和SAPO-34分别作为优化助剂和载体制备得到的Co-Fe/SAPO-34催化剂具有最高的催化活性,在450℃时,NO_x的最大转化率可以达到52.7%.CO_2对Co-Fe/分子筛催化剂活性无明显抑制作用,H_2O对催化剂的活性抑制是可逆的,SO_2对催化剂活性抑制作用明显.Co-Fe/SAPO-34催化剂表面钴物种以CoO和Co(OH)_2为主,Co-Fe/ZSM-5催化剂表面钴物种则以Co_3O_4和Co(OH)_2为主,Co-Fe/Beta催化剂则可能以CoO、Co Al2O_4和Co_3O_4为主.各Co-Fe/分子筛催化剂表面Fe~(2+)/Fe~(3+)含量比依次为Co-Fe/ZSM-5(3.98)>Co-Fe/SAPO-34(0.52)>Co-Fe/Beta(0.43).活性组分钴物种的形态和合适的Fe~(2+)/Fe~(3+)含量比对Co-Fe/分子筛催化剂上甲烷催化还原NO_x至关重要.Co-Fe/分子筛催化剂上CH_4-SCR反应机制为:NO在Br?nsted酸位上吸附氧化成NO~+,同时CH_4在Br?nsted酸位上吸附活化成—C=O和—COO等活性物种,生成的NO~+在Co2+和Fe~(3+)等催化活性位上转化成硝酸盐等中间产物,中间产物硝酸盐与活化物种(—C=O和—COO)反应生成N_2和CO_2.
A series of Co-based / molecular sieve catalysts were prepared by the co-impregnation method. The catalytic behavior of different catalysts in the catalytic reduction of NO x in methane was investigated in a fixed-bed catalytic reactor. The catalysts and carriers for Co-based / The results show that the Co-Fe / SAPO-34 catalyst prepared by Fe and SAPO-34 respectively as the optimization assistant and carrier has the highest catalytic activity. At 450 ℃, the maximum conversion of NO_x The rate can reach 52.7% .CO_2 has no obvious inhibitory effect on the activity of Co-Fe / zeolite catalyst, the inhibition of H_2O on the activity of the catalyst is reversible, and the inhibition of SO_2 on the activity of the catalyst is obvious. The cobalt species on the surface of Co-Fe / SAPO-34 catalyst CoO and Co (OH) 2, Co-3O 4 and Co (OH) 2 are the main types of Co-Fe / ZSM-5 catalysts and CoO, Co Al 2 O 4 and Co 3 O 4 The Fe 2 + / Fe 3+ ratios of Co-Fe / zeolite catalysts were Co-Fe / ZSM-5 (3.98)> Co-Fe / SAPO-34 (0.52)> Co- Fe / Beta (0.43) .The morphology of the cobalt species of the active component and the suitable Fe 2 + / Fe 3+ content ratio on the catalytic activity of methane on the Co-Fe / zeolite catalyst The original NO_x is very important.The reaction mechanism of CH_4-SCR on Co-Fe / zeolite catalysts is as follows: NO is oxidized to NO ~ + on Br? Nsted acid sites and CH_4 is activated on Br? Nsted acid sites to -C = O and -COO and other active species, the generated NO ~ + is transformed into nitrate and other intermediate products at the catalytically active sites such as Co2 + and Fe ~ (3+). The intermediates nitrate and activated species (-C = O and -COO ) Reaction generates N_2 and CO_2.