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Deoxygenation and hydrogenation of biomass-derived molecules over multifunctional catalysts

机译：生物质衍生分子在多功能催化剂上的脱氧和氢化

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The aim of this work was to investigate heterogeneous catalysis of the deoxygenation of renewable feedstocks for value-added chemicals and fuels using heteropoly acids. The main focus was on H3PW12O40 (HPW) and its Cs acidic salt Cs2.5H0.5PW12O40 (CsPW), which have sufficiently high thermal stability, with decomposition temperatures of 450 and > 500 °C, respectively. These compounds have very strong Brønsted acidity and are well documented as acid catalysts. They were used for the deoxygenation and hydrogenation of propionic acid, methyl isobutyl ketone (MIBK) and diisobutyl ketone (DIBK) in the gas phase. For comparison, zeolite catalysts doped with Pt were examined for the deoxygenation of MIBK. CsPW was doped with Pd, Pt, Cu and Ru metals using the impregnation method, while Pt was doped on zeolites by ion exchange. The catalysts under study were characterised using various physical and chemical techniques. CsPW and CsPW-supported Pd, Pt and Cu catalysts were found to be stable in the deoxygenation of propionic acid. They retained the Keggin structure of their polyanion (primary structure), as well as the CsPW crystal structure (secondary structure), after reaction at 400 °C in H2, whereas HPW decomposed above 350 °C in N2. The reaction was found to involve several pathways including ketonisation, decarbonylation, decarboxylation and hydrogenation, leading to the partial or total deoxygenation of propionic acid. HPW/SiO2 and CsPW, both in H2 and in N2, exhibited ketonisation activity between 250 and 300 °C to yield 3-pentanone, CsPW being more selective than HPW. At 400 °C, HPW and CsPW were active for the decarbonylation and decarboxylation of propionic acid to yield ethene and ethane respectively. Loading Pd or Pt onto CsPW greatly enhanced decarbonylation in flowing H2, but had little effect in N2. Similar performance was exhibited by Pd and Pt on SiO2, giving almost 100% selectivity to ethene in H2. These results are consistent with the hydrodeoxygenation of propionic acid on Pd and Pt, suggesting that hydrogenolysis of the C-C bond plays an essential role. Cu catalysts were active in the hydrogenation of the C=O bond to yield propanal and 1-propanol. Turnover rates of propionic acid conversion on metal catalysts followed the order Pd > Pt > Cu. Pt/CsPW was found to be a very efficient catalyst for the selective one-step hydrodeoxygenation of biomass-derived aliphatic ketones MIBK and DIBK to yield 2-methylpentane (MP) and 2,6-dimethylheptane (DMH) under mild conditions at 100 °C and 1 bar pressure without isomerisation of the carbon backbone via a metal-acid bifunctional mechanism. For MIBK hydrogenation, the mechanism involves MIBK hydrogenation to MP-ol on metal sites followed by MP-ol dehydration on acid sites to form olefin and finally olefin hydrogenation to 2MP on metal sites. Pt/ZSM-5 matched the catalytic performance of Pt/CsPW at 200 °C, but considerable isomerisation of MP took place at this temperature. This shows that the strong acidity of CsPW is essential for the high efficiency of the Pt/CsPW catalyst.
机译：这项工作的目的是研究使用杂多酸对增值化学品和燃料的可再生原料进行脱氧的非均相催化。主要关注点是H3PW12O40（HPW）及其Cs酸性盐Cs2.5H0.5PW12O40（CsPW），它们具有足够高的热稳定性，分解温度分别为450和> 500°C。这些化合物具有很强的布朗斯台德酸度，并且已被证明是酸催化剂。它们用于气相中丙酸，甲基异丁基酮（MIBK）和二异丁基酮（DIBK）的脱氧和氢化。为了比较，检查了掺杂Pt的沸石催化剂的MIBK的脱氧。 CsPW采用浸渍法掺杂了Pd，Pt，Cu和Ru金属，而Pt通过离子交换掺杂在沸石上。使用各种物理和化学技术对正在研究的催化剂进行了表征。发现CsPW和CsPW负载的Pd，Pt和Cu催化剂在丙酸的脱氧中是稳定的。在H2中在400°C下反应后，它们保留了其聚阴离子的Keggin结构（一级结构）以及CsPW晶体结构（二级结构），而HPW在N2中在350°C以上分解。发现该反应涉及几种途径，包括酮化，脱羰基，脱羧和氢化，导致丙酸的部分或全部脱氧。 H2和N2中的HPW / SiO2和CsPW在250至300°C之间均显示出酮化活性，生成3-戊酮，CsPW比HPW更具选择性。在400°C时，HPW和CsPW对丙酸的脱羰和脱羧有活性，分别生成乙烯和乙烷。将Pd或Pt负载到CsPW上可大大增强流动的H2中的脱羰作用，但对N2的影响很小。 Pd和Pt在SiO2上表现出相似的性能，从而对H2中的乙烯具有几乎100％的选择性。这些结果与丙酸在Pd和Pt上的加氢脱氧反应一致，表明C-C键的氢解起着至关重要的作用。 Cu催化剂在C ＝ O键的氢化中具有活性，以产生丙醛和1-丙醇。丙酸在金属催化剂上的转化率遵循Pd> Pt> Cu的顺序。 Pt / CsPW被发现是一种非常有效的催化剂，用于在温和的条件下于100°C下对生物质衍生的脂肪族酮MIBK和DIBK进行选择性的一步加氢脱氧生成2-甲基戊烷（MP）和2,6-二甲基庚烷（DMH）。 C和1 bar压力下，碳-骨架不会通过金属-酸双功能机理异构化。对于MIBK氢化，其机理包括MIBK在金属位点氢化为MP-ol，然后在酸性位点进行MP-ol脱水以形成烯烃，最后在金属位点将烯烃氢化为2MP。 Pt / ZSM-5在200°C时的催化性能与Pt / CsPW相当，但是在此温度下MP发生了相当大的异构化。这表明，CsPW的强酸性对于Pt / CsPW催化剂的高效率至关重要。

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    Alotaibi M;

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  • 年度 2000
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