SAPO-34分子筛的合成及用于乙醇脱水的研究

磷酸铝系列分子筛是八十年代开发的新一代分子筛.SAPO-34分子筛是其中的一个成员.SAPO-34属于小孔,大分子不能进入孔道,孔道为三维结构,又无大笼,因此容易结碳的稠环化合物不会形成.由于孔道较小,在C_1分子的催化反应、甲醇脱水制乙酸及甲醇转化成低碳烯烃等方面的应用研究已有较多的报道,但乙醇分子能否顺利进行反应则尚未见报导.考虑到石油资源不丰富的地区以乙醇为化工原料的开发工作有着重要意义,我们研究了乙醇在SAPO-34分子筛上的脱水反应.     

热处理对HZSM-5结构、酸性及催化乙醇脱水反应性能的影响

对商用HZSM-5分子筛进行高温热处理,利用X射线衍射(XRD)、核磁共振波谱法(²⁷Al-MAS NMR)低温氮吸附、电感耦和等离子体放射光谱(ICP-AES)、氨-程序升温脱附(NH₃-TPD)和吡啶吸附傅里叶变换红外(FT-IR)光谱等技术对高温热处理改性前后样品进行了表征,并考察了高温热处理对分子筛的结构、酸性及催化乙醇脱水制乙烯反应性能的影响。结果表明,热处理改性后的HZSM-5分子筛发生骨架脱铝,B酸减少,L酸增多,孔容增大,出现新的介孔;适中的酸性位和复合型的介-微双孔道结构使其减少了反应中的副反应,乙烯的选择性得到提高,催化剂寿命显著提高。     

对五氧化二磷催化乙醇脱水反应的研究

研究了不同反应条件下用P2O5催化乙醇脱水反应的情况,并用GC和GC-MS方法检测反应产物。为苏教版《有机化学基础》教材中“认识乙醇的脱水反应”提供教学参考。     

无水三氯化铝催化乙醇脱水反应制乙烯的实验研究

针对浓硫酸或五氧化二磷作催化剂的不足,该研究采用无水三氯化铝催化乙醇制乙烯,可使反应体系在120~130℃左右产生大量乙烯气体。同时从理论上探究了无水三氯化铝催化乙醇脱水的机理,并从教学演示实验的角度改进了反应装置,取得了较好的实验效果。     

生物质乙醇在 Fe-HZSM-5分子筛催化剂上脱水制乙烯

乙烯是一种重要的大宗化工原料.目前国内外乙烯的生产方法主要是石脑油裂解法.但是,随着全球性石油资源供求关系日趋紧张,以及该生产过程存在较大环境污染,该工艺面临严峻挑战.生物乙醇是一种可以通过生物质发酵获得的可再生资源.因此,生物质乙醇催化脱水制乙烯工艺受到越来越多研究者关注.该技术的关键在于高性能乙醇脱水制乙烯催化剂的开发.研究发现, Si/Al比大于40的 Fe改性 ZSM-5分子筛在乙醇转换制碳氢化合物的催化反应中具有较高活性,当反应温度大于400oC时,可生成 C1-C9的烷烃、烯烃和芳香烃,其中以 C3产物和芳香烃产物为主.本文研究了 Si/Al比为25-300的 Fe离子交换 ZSM-5分子筛在乙醇脱水制乙烯反应中的催化活性,并利用 XRD, NH3-TPD,吡啶吸附 FT-IR和DRS UV-VIS等表征手段,研究了催化剂的晶相结构、表面组成及酸性位点等,进而探究了该催化反应的反应机理.我们首先考察了 Si/Al比为25-300的 HZSM-5分子筛.随着分子筛 Si/Al比增大,乙醇转化率先增加后降低,在 Si/Al比为100时获得最高值;但是乙烯收率随着 Si/Al比的增加而持续下降, Si/Al比为25时有其最高值47%.经产物分析, HZSM-5(25)和 HZSM-5(300)虽具有相似的乙醇转化率,但前者产生大量 C3+产物,而后者产物只有乙烯和乙醚.据文献报道,乙醚是乙醇脱水制乙烯的中间产物,它的进一步脱水产生乙烯,而乙烯可进一步转化生成 C3+产物.因此,由于 HZSM-5(300)表面酸性较弱,主要生成反应中间体,而 HZSM-5(25)较强的表面酸性又导致乙烯进一步转化,生成 C3+产物.然后我们考察了经过3次离子交换处理的 Fe-ZSM-5催化剂.随着 Si/Al比上升(25-300),乙醇转化率和乙烯收率下降, Si/Al比为25时为其最高值;随着反应温度上升,乙醇转化率在260oC时达到近100%,之后维持不变,乙烯收率也在260 oC时为其峰值,温度继续上升造成乙烯收率再次下降;催化剂空速增大降低乙醇转化率和乙烯收率.经产物分析,温度较低和空速较大时产生大量的反应中间体乙醚,而温度较高时导致乙烯进一步转化生成 C3+产物.在反应温度为260oC、空速为0.81 h-1时, Fe-HZSM-5(25)催化剂上乙醇转化率为98%-99%、乙烯收率为97%-99%,并可实现长达1440 h的单程使用寿命,该值是 HZSM-5(25)催化剂的20余倍,具有很好的工业应用前景.为探究 Fe-ZSM-5(25)催化剂高催化活性和长催化寿命的原因,我们表征了催化剂.从 XRD结果可以看出,离子交换没有损坏 HZSM-5的晶体结构,也没有新的可检测到的物相产生.从 NH3-TPD结果看, HZSM-5(25)的CH/CL(强酸/弱酸)比为0.7, Fe-ZSM-5(25)的CH/CL比为0.29,可知 Fe离子交换降低了分子筛的表面酸性,特别是强酸性位.从吡啶吸附 FT-IR结果看, HZSM-5(25)的 B/L (Br?nsted酸性位/Lewis酸性位)比为1.42, Fe-ZSM-5(25)的 B/L比为0.25,可知 Fe离子交换主要减少的是分子筛表面的 Br?nsted酸性位.文献报道,乙醇脱水制乙烯主要发生在弱酸性位上,而乙烯进一步转化为 C3+产物发生在强酸性位上.所以,催化剂上强酸性位的减少有利于乙烯的生成反应.另据文献报道, Br?nsted酸性位是乙烯聚合、迅速覆盖催化活性位点产生积炭的催化活性中心.因此, Br?nsted酸性的降低可认为是 Fe-HZSM-5(25)催化剂单程使用寿命长较 HZSM-5(25)分子筛显著延长的原因.从 UV-VIS结果得知, Fe-ZSM-5上的 Fe物种主要以骨架内和骨架外 Fe3+为主,此外含有少量低聚合的 FexOy,但几乎没有 Fe2O3颗粒存在.文献记载, Fe3+物种是乙烯形成的活性物种,而 FeOx催化产生乙烯和乙醛.因此,催化剂中大量骨架内和骨架外 Fe3+物种的存在也可认为是该催化剂具有较强乙醇脱水制乙烯催化活性的原因之一.     

生物乙醇催化脱水制乙烯的研究进展

阐述了利用生物质能源的重要性,介绍了生物乙醇催化脱水制乙烯的发展现状,特别是其催化剂的研究状况。针对乙醇脱水制乙烯催化剂存在的问题,提出当前催化剂的发展趋势。     

改性膨润土催化乙醇流化床脱水制乙烯

以浸渍法制备的改性膨润土为催化剂,在自行设计的流化床装置上评价了乙醇脱水制乙烯的催化性能;采用X-射线衍射（XRD）、傅里叶变换红外（FT-IR）、扫描电镜（SEM）、比表面分析（BET）和热重分析（TG）等手段对催化剂的理化性能进行表征,同时考察了不同催化剂制备条件和催化反应条件等工艺因素对催化剂性能的影响。结果表明,当硫酸质量分数为44％,水洗至pH值为4～5,添加0．15g混合氯化稀土,反应温度为270℃,乙醇的进样流速为013mL／min,催化剂用量3g,催化反应的活性最佳,出口乙烯气体的体积分数可达8．56×10^-1。     

乙醇脱水反应的热力学分析与实验研究

乙醇脱水反应在不同温度条件下可生成不同产物,作者用定压热容计算了两类不同反应的反应热、吉布斯自由能、化学平衡常数,从理论上分析了两种主要反应在不同温度条件下进行的程度及相互竞争的趋势,并通过实验对理论分析进行了验证.     

改性HZSM-5催化乙醇脱水制乙烯的研究

采用离子交换法分别制备了铁、钴、镍改性的HZSM-5分子筛催化剂.在连续流动固定床微型反应装置上对催化剂进行了活性评价,结果表明镍改性的催化剂具有较好的低温活性.采用透射电镜(TEM),X射线衍射(XRD),吡啶程序升温脱附(Py-TPD),N2-吸附脱附和程序升温氧化(TPO)等手段对催化剂反应前后的物性进行了表征,结果表明催化剂的表面酸性决定其催化乙醇脱水的性能.镍改性后,降低了催化剂的强酸量、增加了弱酸量,有利于乙醇转化率和乙烯选择性的提高,镍是比较合适的改性金属.以镍改性的HZSM-5为催化剂,对乙醇脱水制乙烯反应的工艺条件进行了优化.     

Copper-Catalyzed Amination of Aryl Halides with Aqueous Ammonia under Mild Conditions

A Cu(I) generated in situ from CuSO₄·5H₂O/sodium ascorbate catalyzed cross‐coupling reaction of aryl halides with aqueous ammonia for the synthesis of primary aromatic amines has been developed. Key to the success included the application of aqueous ammonia under a homogeneous condition.     

Formamide as an Ammonia Synthon in Amination of Acid Chlorides

The use of formamide as a convenient source of ammonia has been explored for the direct transformation of acid chlorides to primary amides. Various aliphatic, alicyclic aromatic, and heterocyclic acid chlorides are converted to the corresponding carboxamides in good yields (75–94%).     

Nickel‐Catalyzed Amination of Aryl Chlorides with Ammonia or Ammonium Salts

The nickel‐catalyzed amination of aryl chlorides to form primary arylamines occurs with ammonia or ammonium sulfate and a well‐defined single‐component nickel(0) precatalyst containing a Josiphos ligand and an η²‐bound benzonitrile ligand. This system also catalyzes the coupling of aryl chlorides with gaseous amines in the form of their hydrochloride salts.     

Electrochemical Desulfurizative Amination of Heteroaromatic Thiols by Iodine Catalysis

N-Heterocyclic amines have been known as an important class of nitrogen-containing molecules with a wide range of applications. Described here is a mild and efficient electrochemical desulfurizative amination of readily accessible heteroaromatic thiols without necessity of metal catalyst. The key to success for this reaction is the in-situ generation of a hypervalent iodine reagent as an organocatalyst from iodoarene by anodic oxidation. This mild desulfurizative amination presents ample substrate scope and good functional group tolerance without the use of extra stoichiometric chemical oxidants. As only electrons serve as the oxidation reagents, this method offers a straightforward and sustainable manner towards versatile N-heterocyclic amines, including late-stage functionalization of pharmaceutically relevant molecules.     

表面光电压谱在稀土杂多酸催化研究中的应用

表面光电压法早巳用于研究半导体能带分布及表面态,但尚未见用于研究催化作用的报道。我们在自装的光电压谱仪上,对结构相似的系列稀土硅钨酸催化剂进行了研究,对其表面电荷(表面能级)的微小差异在催化反应中的作用有了新的认识。     

Earth-abundant Metal-catalyzed Reductive Amination: Recent Advances and Prospect for Future Catalysis

Nitrogen-containing compounds, as an important class of chemicals, have been used widely in pharmaceuticals, materials synthesis. Transition metal-catalyzed reductive amination of an aldehyde or a ketone with ammonia or an amine has been proved to be an efficient and practical method for the preparation of nitrogen-containing compounds in academia and industry for a century. Given the above, several effective methods using transition metals have been developed in recent years. Noble transition metals like Pd, Pt, and Au-based catalysts have been predominately used in reductive amination. Because of their high prices, strict official regulations of residues in pharmaceuticals, and deleterious effects on the biological system, their industrial applications are severely hampered. With the increasing sustainable and environmental problems, the Earth-abundant transition metals including Ti, Fe, Co, Ni, and Zr have also been investigated for the reductive amination reaction and showed great potential to the advancement of sustainable and cost-effective reductive amination processes. This critical review will mainly summarize the work using Earth-abundant metals. The effects of different transition metals used in catalytic reduction amination were discussed and compared, and some suggestions were given. The last section highlights the catalytic activities of bi- and tri-metallic catalysts. Indeed, this latter family is very promising and simultaneously benefits from increased stability, and selectivity, compared to monometallic NPs, due to synergistic substrate activation. Few comprehensive reviews focusing on Earth-abundant transition metals catalyst has been published since 1948, although several authors reported some summaries dealing with one or the other part of this aspect. It is hoped that this critical review will inspire researchers to develop new efficient and selective earth-abundant metal catalysts for highly, environmentally sustainable reductive amination methods, as well as improve the pharmaceutical industry and related chemical synthesis company traditional method with the utilization of the green method widely.     

Reductive Amination by Photoredox Catalysis and Polarity‐Matched Hydrogen Atom Transfer

The excitation of a Ru^II photosensitizer in the presence of ascorbic acid leads to the reduction of iminium ions to electron‐rich α‐aminoalkyl radical intermediates, which are rapidly converted into reductive amination products by thiol‐mediated hydrogen atom transfer (HAT). As a result, the reductive amination of carbonyl compounds with amines by photoredox catalysis proceeds in good to excellent yields and with broad substrate scope and good functional group tolerance. The three key features of this work are 1) the rapid interception of electron‐rich α‐aminoalkyl radical intermediates by polarity‐matched HAT in a photoredox reaction, 2) the method of reductive amination by photoredox catalysis itself, and 3) the application of this new method for temporally and spatially controlled reactions on a solid support, as demonstrated by the attachment of a fluorescent dye on an activated cellulose support by photoredox‐catalyzed reductive amination.     

锌在ZnZSM-5沸石中的形态及其催化作用

采用NH_3－TPD和吡啶吸附红外光谱法，研究了不同含Zn量ZnHZSM-5沸石中Zn的存在状态．结果表明，用浸渍方式将Zn引入到HZSM-5沸石后，在NH_3－TPD谱上产生两个新的NH_3脱附峰．峰位分别在原HZSM－5沸石的低温峰与高温峰之间和比高温峰较高温区处，其相应的吸附中心分别以L_1、L_2表示．L_1可能与ZnHZSM－5沸石上ZnO物种相对应; L_2与吡啶吸附红外光谱的L_(1616)吸收带有关，可能与ZnHZSM-5上的ZnOH~＋物种相对应．丙烷芳构化反应结果表明，芳烃收率随L_2的脱附NH_3量的增加有一最宜值，而活性的稳定性则随之降低。