磷酸化Ti、Zr复合金属氧化物催化六碳糖转化制备5-羟甲基糠醛

Conversion of Hexose to 5-Hydroxymethylfurfural Catalyzed by Phosphated Binary Ti-Zr Oxide

纤维素等碳水化合物可通过脱水转化制备一种重要的生物燃料前驱体——5-羟甲基糠醛(HMF)。以钛酸异丙酯和正丁醇锆作为前驱体,按不同物质的量之比制备含有Ti、Zr的复合金属氧化物(TiZrO)的催化剂,并引入P元素以强化催化剂酸性,得到催化剂TiZrPO,当n(Ti)∶n(Zr)为7∶3、1∶1与3∶7时,分别制得催化剂TiZrPO-1、TiZrPO-2和TiZrPO-3,通过XRF、STEM、FT-IR和NH 3-TPD分析方法对催化剂结构进行了表征,并考察了170℃条件下催化剂对果糖和葡萄糖催化转化制备HMF的性能。催化剂表征结果显示:Ti、Zr、P元素均匀地分布在催化剂中,通过控制催化剂中的Ti、Zr比例能够调节催化剂的Br nsted酸(B酸)和Lewis酸(L酸)分布,其中当Ti、Zr元素物质的量之比为1∶1时,催化剂TiZrPO-2中的B酸酸量最高为2.55μmol/g,B酸与L酸酸量比值达到最高为0.49。催化果糖和葡萄糖转化制备HMF结果显示TiZrPO-2的催化性能最优,催化40 min时,果糖转化率为98.5%,HMF产率为76.5%;催化180 min时,葡萄糖转化率为72.2%,HMF产率为38.1%;当循环使用4次时,果糖和葡萄糖转化率仍达92.7%和65.8%,对应的HMF产率分别为72.6%和30.4%,TiZrPO-2表现出较好的重复使用性能。结合葡萄糖转化过程中果糖、左旋葡聚糖等产物分析结果,发现L酸能够促进葡萄糖向果糖的转化,但同时也会导致果糖发生副反应;B酸能够促进葡萄糖脱水生成左旋葡聚糖,同时也可以催化果糖和葡萄糖直接脱水生成HMF。

5-hydroxymethylfurfural(HMF),an important precursor for biofuel production,can be prepared via dehydration of carbonhydrates such as cellulose.In this study,titanium tetraisopropanolate and zirconium n-butoxide with different molar proportion were used as the precursor to prepare binary oxides(TiZrO).Phosphorus was introduced to enhance the acidity of catalyst and to obtain TiZrPO.TiZrPO-1,TiZrPO-2 and TiZrPO-3 catalysts were prepared,when n(Ti)∶n(Zr)was 7∶3,1∶1 and 3∶7,respectively.The structures of these catalysts were characterized by XRF,STEM,FT-IR and NH 3-TPD,and the catalytic performance for the conversion of fructose and glucose to HMF was tested.The characterization results suggested that Ti,Zr and P distributed evenly in the catalysts.Moreover,the distribution of Br nsted acid and Lewis acid could be controlled by adjusting the value of n(Ti)∶n(Zr).When n(Ti)∶n(Zr)was 1∶1,the amount of Br nsted acid reached the maximum(2.55μmol/g)in TiZrPO-2,and the corresponding Br nsted acid to Lewis acid ratio(0.49)was also the highest.The catalytic performance of TiZrPO on the conversion of fructose and glucose showed that,among the three catalysts,TiZrPO-2 had the best catalytic performance with 98.5%conversion of fructose and 76.5%yield of HMF at 40 min,and 72.2%conversion of glucose and 38.1%yield of HMF at 180 min;when TiZrPO-2 was recycled and reused for 4 times,the conversions of fructose and glucose still reached as high as 92.7%and 65.8%,respectirely.While the corresponding HMF yields were 72.6%and 30.4%,respectively,which indicated that TiZrPO-2 had satisfying reusability.According to the product analysis for fructose,levoglucosan,etc.,it was found that Lewis acid could promote the conversion of glucose to fructose,while side reactions involving fructose was also favored.Br nsted acid could accelerate the dehydration of glucose to levoglucosan,and it also catalyzed the direct dehydration of fructose and glucose to HMF.