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针对从简单铝盐(AlCl3,Al(NO3)3等)体系中制备化学品氧化铝易发生凝聚而导致颗粒分散性差的问题,提出利用柠檬酸作为铝的络合剂,并采用碳酸铝铵(AACH)作为中间体制备多孔氧化铝的方法。将柠檬酸铝溶液调节到一定pH值后,滴加到碳酸氢铵溶液中可以得到结晶良好的AACH固体,再通过简单焙烧后即可得高比表面积的多孔球型Al2O3产品。通过对原料碳酸氢铵和柠檬酸铝的物质的量之比β、反应体系pH值、反应温度及陈化时间对铝转化率α的影响的研究发现,在β=2,pH=9,室温25℃,陈化8 d,有50%的柠檬酸铝转化为AACH。同时推测出,由于AACH的形成受柠檬酸,铝酸钠,碳酸氢铵三重络合-缓冲体系的限制,首先需要调节柠檬酸铝,其pH值大于9后缓慢释放出Al(OH)4-,Al(OH)4-再同碳酸氢铵反应易得到结晶良好的AACH晶体。TG-DTA热分析和XRD测试表明:300℃下AACH可完全分解为不定型氧化铝,700和1400℃下焙烧可分别得到γ-Al2O3,α-Al2O3。SEM和TEM测试表明,所得AACH粒径约为15μm,并由大量长度为500 nm左右的纳米棒组成,700℃焙烧后得到形貌不变,含有大量孔径为1～5 nm微孔、BET比表面积为235 m2.g-1的多孔氧化铝。
Aiming at the problem that alumina is easy to aggregate due to the preparation of chemical aluminum AlCl3, Al (NO3) 3 and so on, which leads to poor particle dispersibility, citric acid is proposed as a complexing agent of aluminum and aluminum ammonium carbonate AACH) as an intermediate to prepare porous alumina. After the aluminum citrate solution is adjusted to a certain pH value, a well-crystallized AACH solid can be obtained by dropping into the ammonium bicarbonate solution, and then a porous spherical Al2O3 product with a high specific surface area can be obtained by simple calcination. Through the study of the effect of the ratio of the amount of raw material ammonium bicarbonate and aluminum citrate on the aluminum conversion rate, β, the reaction system pH value, the reaction temperature and the aging time, it was found that when β = 2, pH = 9, 25 ℃, aging 8 d, 50% aluminum citrate into AACH. At the same time it is inferred that due to the formation of AACH by citric acid, sodium aluminate, ammonium bicarbonate triple complex - buffer system, the first need to adjust the aluminum citrate, the pH is greater than 9 and slowly released Al (OH) 4- , Al (OH) 4 - again with ammonium bicarbonate reaction easy to get well-crystallized AACH crystal. TG-DTA thermal analysis and XRD results show that AACH can be completely decomposed into amorphous alumina at 300 ℃, and γ-Al2O3 and α-Al2O3 can be obtained by calcination at 1400 and 1400 ℃, respectively. The results of SEM and TEM showed that the obtained AACH particles were about 15μm in size and consisted of a large number of nanorods with a length of about 500 nm. After being calcined at 700 ℃, Porous alumina with a surface area of 235 m2.g-1.