Aldol Condensations on Solid Catalysts: A Cooperative Effect between Weak Acid and Base Sites

An amorphous aluminophosphate (ALPO) catalyst containing weak acid and base centers can carry out the aldol condensation of heptanal with benzaldehyde at much higher rates and selectivities than conventional solid acid (amorphous or crystalline aluminosilicates) or base catalysts (MgO, hydrotalcites, KF/Al₂O₃, nitrurated ALPO). With the weak acid‐base catalyst, the reaction occurs through a bifunctional acid‐base mechanism that involves the activation of benzaldehyde, by protonation‐polarization of the carbonyl group on the acid sites, and the attack of the enolate heptanal intermediate generated on the basic sites. With this type of bifunctional acid‐base catalyst, compounds with weak basicities are already able to undergo the reaction with a much higher selectivity than those obtained on stronger acid or base catalysts.     

Condensation of citral and ketones using activated hydrotalcite catalysts

Activated hydrotalcite catalysts were prepared via calcination and room-temperature rehydration. Replacement of water from the pores after rehydration resulted in an increased amount of accessible active sites. The performance of the catalyst was explored in liquid-phase aldol condensations at low temperatures. In the citral–acetone condensation high activities and selectivities were obtained. Usage in the citral–MEK condensation showed also a high citral conversion, with methyl pseudoionones as primary products.     

Base-catalyzed condensation of citral and acetone at low temperature using modified hydrotalcite catalysts

A study on the catalytic properties of properly activated hydrotalcite (HT) with special attention to the nature and amount of active sites present in this solid base catalyst has been undertaken. Only a small fraction (5%) of the available basic sites in the rehydrated calcined HT is active in liquid-phase aldol condensations. These sites exhibit high catalytic activity and are most likely localized at the edges of the HT-platelets. Besides a high activity, these modified HTs also show a high selectivity. No further condensation products other than diacetone alcohol (DAA) in the acetone self-condensation could be observed. Initial results with the citral–acetone condensation show that even at 273 K this reaction is catalyzed by modified HTs with a conversion of 65% and a selectivity of 90%, when the citral concentration is not too high (1 wt.%). At higher citral concentrations, no reaction is observed indicating a negative order in citral concentration.     

Catalytic synthesis of chalcone and flavanone using Zn–Al hydrotalcite adhere ionic liquid

The Claisen–Schmidt condensation of 2′-hydroxy acetophenone and benzaldehyde to chalcone and flavanone show that calcined Zn–Al (6) hydrotalcite is active for this synthesis. Coating of ionic liquid ‘1-(tri-ethoxy-silyl-propyl)-3-methyl-imidazolium chloride’ on Zn–Al hydrotalcites was accomplished employing incipient wetness process and on NaY, NaX, MK-5 and silica gel employing co-condensation methodology. Impregnated IL on calcined Zn–Al (6) catalysts were characterized by XRD, SEM, BET, ¹³C and ²⁷Al NMR analysis and the activity of these catalysts were investigated for chalcone and flavanone synthesis. ²⁷Al CP MAS NMR technique was used to show that interaction of IL with hydrotalcite modifies the acid–base sites and is responsible for enhancement of catalyst activity. Several aromatic aldehydes were screened to assess the general applicability of the system.     

Solid catalysts for the production of fine chemicals: the use of ALPON and hydrotalcite base catalysts for the synthesis of arylsulfones

α#x2010;phenylsulfonylcinnamononitrile and derivatives as well as α-phenylsulfonylchalcone have been obtained by condensation of phenylsulfonylacetonitrile and phenylsulfonylacetophenone with benzaldehyde and 4-substituted benzaldehydes, using solid base catalysts with different basic strengths. Cs-exchanged X zeolite showed low activity for the above reactions, while high-surface-area MgO and MgO–Al₂O₃ mixed oxides derived from hydrotalcite were active and selective catalysts. An optimum basicity was observed with MgO–Al₂O₃ with the atomic ratio Al/(Al+Mg) between 0 and 0.20, showing the increase in basicity when introducing Al in the MgO structure. Nitridation of a high-surface-area aluminophosphate gives active and selective catalysts for the above reactions. The activity per unit surface area for the less demanding reaction between sulfonylacetonitrile and benzaldehyde is directly proportional to the level of nitridation. However, formation of α-phenylsulfonylchalcone, which is a more demanding reaction, does not increase linearly but goes through a maximum with the nitrogen content of the solid, showing the heterogeneity of active sites on ALPONs and the decrease in the activity coefficient of the basic sites when the density of N atoms increases. This revised version was published online in July 2006 with corrections to the Cover Date.     

Aluminophosphates Oxynitrides as Base Catalysts for the Production of Dicyanomethylene Derivative Dyes

The two-step synthesis of dicyanomethylene derivative dyes has been performed using as base catalysts MgO, calcined hydrotalcites and ALPON. These solids catalyse with good conversions and selectivities the Knoevenagel reaction step, but only ALPON catalysts are able to catalyse efficiently the two reaction steps, as well as the global reaction in a one-pot system.     

固体碱催化丙酮和碳酸二甲酯合成乙酰乙酸甲酯

以碳酸二甲酯(DMC)与丙酮为原料,在固体碱上合成乙酰乙酸甲酯,并考察了反应温度、反应时间、催化剂用量和原料摩尔比等因素对反应结果的影响。结果表明,以固体酸为催化剂时,无乙酰乙酸甲酯的生成,而具有中强碱位的K/MgO对反应具有较好的催化性能。当以K/MgO为催化剂,在反应温度为240℃,反应时间5h,催化剂用量为反应物总质量的1.5%,原料摩尔比为n(丙酮)∶n(DMC)=1∶4时,丙酮的转化率和乙酰乙酸甲酯的选择性分别达到41.2%和50.3%。反应的主要副产物为丙酮自身缩合的产物(二丙酮醇、4-甲基-3-烯基-2-戊酮、4-甲基-4-烯基-2-戊酮)以及醚化产物(2-甲氧基丙烯)等。     

复原镁铝水滑石固体碱在Aldol反应中的应用

以镁铝水滑石为前体焙烧制得镁铝复合氧化物,在含水体系中水合催化取代苯甲醛和丙酮的aldol反应。结果显示,水滑石前体经过复原处理后活性高于普通Mg/Al水滑石;Mg/Al比为4∶1,NaOH/Na2CO3为沉淀剂,镁铝的硝酸盐作为金属盐来源制备的催化剂对对硝基苯甲醛和丙酮之间的aldol反应具有最好的催化效果。     

The impact of the “memory effect” on the catalytic activity of Mg/Al; Mg,Zn/Al; Mg/Al,Ga hydrotalcite-like compounds used as catalysts for cycloxene epoxidation

The epoxidation of cyclohexene by hydrogene peroxide and benzonitrile, in methanol as solvent on solid base catalysts, hydrotalcites (HT) and corresponding mixed oxides (C-HT) was investigated. The employed catalysts were as-synthesized Mg/Al; Mg,Zn/Al; Mg/Ga,Al hydrotalcites, their derived mixed oxides and the corresponding reconstructed hydrotalcite forms (R-HT) obtained via the “memory effect” upon a rehydration treatment of C-HT. The catalysts were characterized by XRD, CO₂-TPD and N₂ adsorption–desorption measurements.

The reconstructed HT samples exhibit higher activity in comparison to the as-synthesized carbonated HT samples. A tentative correlation of the catalytic properties with the base strength of the active sites, the structural and textural characteristics of the catalysts, has been explored.     

Ortho-alkylation of phenol derivatives with methanol over magnesium oxide catalysts. 1. Characterization of promoted magnesium oxide catalysts

Cr- and Pt-promoted magnesium oxide catalysts were used to catalyze ortho-alkylation of phenol derivatives in the presence of excess methanol. The characteristic properties of the MgO surface measured by XRD, SEM, BET, and TPD suggest that Cr exists as fine chromium oxide particles on the MgO surface, while a Pt and MgO interaction causes an increase of the BET surface area as well as of surface acid and base amounts. Cr/MgO shows a specialty for ortho-alkylation of phenol derivatives with methanol without forming O-alkylated products, i.e., anisole or methylated anisole. The catalytic activity and the stability of Cr/MgO are improved by the addition of a fairly small amount of Pt. The effect of Pt can be explained by the Pt and MgO interaction which increases both the acid and base amounts. A mechanism involving the reaction of phenol derivatives and methanol adsorbed simultaneously on acid–base pair sites is proposed.     

超声辐射下n(Mg)∶n(Al)水滑石催化合成

通过低饱和共轭沉淀法制备了不同n(Mg)∶n(Al)的水滑石，并用XRD和BET等技术对催化剂前驱体进行了表征。XRD表征表明，水的加入使得水滑石的结构能够得到部分重建。同时水的加入使水滑石表面的O^2- 生成了相应的B碱(OH^-)，大大提高了催化活性。BET表征结果表明，水滑石作为碱性催化剂的活性位点主要存在于暴露的板层边缘。以制备的水滑石为催化剂在超声辐射下合成了含有强吸电子取代基4,4′-二硝基查尔酮，并考察了超声、催化剂的组成、水合质量和溶剂对催化性能的影响。结果表明，当催化剂的n(Mg)∶n(Al)＝3.0、水合质量为其前驱体的35％和溶剂为甲醇时，在超声辐射下具有最高的催化活性，收率达91.3%，选择性为100%。     

固体碱催化合成假性紫罗兰酮研究

采用自制的固体碱催化剂KF/Al2O3-MgO催化柠檬醛与丙酮的缩合反应,成功合成了假性紫罗兰酮,柠檬醛转化率达到99%,假性紫罗兰酮得率最高达到85%,同时利用正交试验确定出了反应的最佳条件。     

Calcined hydrotalcites for the catalytic decomposition of N2O in simulated process streams

Various hydrotalcite based catalysts were prepared for testing for the catalytic decomposition of N₂O. CoAl, NiAl, Co/PdAl, Co/RhAl, and Co/MgAL substituted hydrotalcites and CoLaAl hydroxides offer very good activity at modest temperatures. Precalcination of these materials at ca. 450–500°C, which destroys the hydrotalcite phase, is necessary for optimum activity and life. For Co substituted hydrotalcites, the optimal ratio of Co/Al is 3.0. The temperature for 50% conversion of N₂O of these calcined cobalt hydrotalcites is ca. 75°C lower than for the previous highly active Co-ZSM-5. These calcined cobalt hydrotalcite materials display sustained life at temperatures in excess of 670°C in an O₂ rich, wet stream with high levels of N₂O [10%]. Excess O₂ does not seriously impact N₂O decomposition, but the combination of both water vapor and O₂ does reduce activity by ca. 50%.     

CoMo/MgO–Al2O3 supported catalysts: An alternative approach to prepare HDS catalysts

Three different supports were prepared with distinct magnesia–alumina ratio x = MgO/(MgO + Al₂O₃) = 0.01, 0.1 and 0.5. Synthesized supports were impregnated with Co and Mo salts by the incipient wetness method along with 1,2-cyclohexanediamine-N,N,N′,N′-tetraacetic acid (CyDTA) as chelating agent. Catalysts were characterized by BET surface area, Raman spectroscopy, SEM-EDX and HRTEM (STEM) spectroscopy techniques. The catalysts were evaluated for the thiophene hydrodesulfurization reaction and its activity results are discussed in terms of using chelating agent during the preparation of catalyst. A comparison of the activity between uncalcined and calcined catalysts was made and a higher activity was obtained with calcined MgO–Al₂O₃ supported catalysts. Two different MgO containing calcined catalysts were tested at micro-plant with industrial feedstocks of heavy Maya crude oil. The effect of support composition was observed for hydrodesulfurization (HDS), hydrodemetallization (HDM), hydrodeasphaltenization (HDAs) and hydrodenitrogenation (HDN) reactions, which were reported at temperature of 380 °C, pressure of 7 MPa and space-velocity of 1.0 h⁻¹ during 204 h of time-on-stream (TOS).     

微波法制备的固体碱催化丁醛自缩合反应

用微波辐射法制备了负载型固体碱催化剂K2 O/γ Al2 O3 、MgO/γ Al2 O3 、KF/γ Al2 O3 、Na2 O/γ Al2 O3 、CaO/γ Al2 O3 和SrO/γ Al2 O3 ,并应用于丁醛的自缩合反应 ,其中K2 O/γ Al2 O3和KF/γ Al2 O3 的活性较好 ,1h产率分别为 5 2 5 %和 4 7 5 %。同时考察了水的浓度及溶剂对反应的影响。结果表明当水的浓度为 1 4mol/L时 ,催化剂的活性最佳 ,而丁醇作为溶剂是几种所用溶剂中最好的一种     

镁铝复合氧化物催化合成丙二醇乙醚

以硝酸镁、硝酸铝和氨水为原料,通过共沉淀方法制备了一系列镁铝水滑石材料,经过焙烧处理后作为碱催化剂用于丙二醇乙醚的催化合成。采用X射线衍射、热分析、SEM、DTA-TG和CO^_2-TPD等手段对所制备的催化剂进行表征,结果表明,在实验范围所制备的催化剂均具有典型的镁铝水滑石结构。采用高压固定床反应器对催化剂进行活性评价,考察了形成沉淀的pH、晶化方式、原料中镁与铝物质的量比及焙烧温度等对镁铝水滑石及其衍生物的结构和催化活性的影响,研究了碱性与催化剂活性之间的关系,结果表明,镁与铝物质的量比为3和550 ℃焙烧的催化剂具有良好的催化合成丙二醇乙醚活性。超声晶化的方式可以提高镁铝水滑石衍生物的碱强度,但对镁与铝物质的量比不同的催化剂活性有着不同的影响。在（350～550） ℃,焙烧温度的提高可以增大催化剂的碱强度和碱量,催化活性也有显著提高,但进一步升高焙烧温度,催化剂的表面碱强度和碱量有所下降,催化活性也随之降低。     

固体碱催化苯乙酮和碳酸二甲酯合成苯甲酸甲酯

以固体酸碱为催化剂,研究了碳酸二甲酯与苯乙酮合成苯甲酸甲酯的反应,考察了反应温度、反应时间、催化剂用量和原料摩尔配比等因素对反应结果的影响。实验结果表明,固体酸催化剂不利于苯甲酸甲酯的生成,而具有中强碱位的MgO对反应有较好的催化活性。当以MgO为催化剂,在反应温度为260℃,反应时间5 h,催化剂用量为反应物总质量的1.5%,n(苯乙酮)∶n(DMC)=1∶4的条件下,苯乙酮的转化率和苯甲酸甲酯的选择性分别达72.0%和59.8%。另外,反应的副产物主要为乙酸甲酯、少量苯乙酮缩合的产物、甲基化及醚化产物等。     

Mg-Al复合氧化物催化材料的制备及表征

采用水热合成法制备了Mg-Al复合氧化物催化剂,考察了模板剂十六烷基三甲基溴化铵(CTAB)用量对水滑石结构的影响。结果表明,加入CTAB的浓度远大于临界胶束浓度时,水滑石呈现棒状结构。将镁铝复合氧化物用于催化豆油与甲醇的酯交换反应,醇/油摩尔比为12∶1,催化剂用量为3%,反应温度65℃和反应时间2 h的条件下,豆油的转化率达78.9%。     

NOx storage/reduction catalysts based in cobalt/copper hydrotalcites

The use of materials based on hydrotalcites as NO_x storage/reduction (NSR) catalysts has been investigated, examining their activity at low temperature and their resistance to poisons such as H₂O and SO₂. The results obtained show that catalysts derived from Mg/Al hydrotalcites containing copper or cobalt is active at low temperatures, specially the samples containing 10 or 15% of Co. The addition of 1 wt% of transition metals with redox properties such as Pt, Pd, V and Ru to the hydrotalcite increases its activity because the combination of the redox properties of these metals and the acid-base properties of the hydrotalcite. The best results were obtained with the catalyst derived from a hydrotalcite with a molar ratio Co/Mg/Al = 15/60/25 and containing 1 wt% V. This material shows a higher activity, at low temperatures and in the presence of H₂O and SO₂, than a Pt–Ba/Al₂O₃ reference catalyst.     

Characterization of bimetallic rhodium-germanium catalysts prepared by surface redox reaction

The preparation of bimetallic rhodium-germanium/silica and rhodium-germanium/alumina catalysts was investigated by controlled surface reaction. Their catalytic performances were measured for two gas phase reactions (toluene hydrogenation at 323 K and cyclohexane dehydrogenation at 543 K) and for a liquid phase reaction (citral hydrogenation at 343 K).

Elemental analysis of bimetallic catalysts showed that germanium can be deposited by redox reaction between hydrogen activated on a parent monometallic rhodium catalyst and germanium tetrachloride dissolved in water (catalytic reduction method). EDX microanalysis of rhodium-germanium/silica catalysts indicated that rhodium and germanium were deposited in close contact on the silica support. However, on alumina-supported catalysts, germanium deposition occurred also separately on the support. For the different test reactions, the catalytic properties of rhodium were strongly altered by the addition of germanium. On alumina-supported catalysts, interesting catalytic effects were observed in citral hydrogenation when not only close contact exists between both metals but when, in addition, the second metal was deposited on the support in the close vicinity of rhodium.