Solvents play a critical role in “greening” synthetic chemistry, and this is also true in catalytic organic synthesis. This review attempts to summarize the progress made in the past a few years on homogeneous and heterogeneous catalytic reactions in the non-conventional solvents, water, ionic liquids, supercritical carbon dioxide and fluorous carbons, with the focus on those catalyzed by transition metal complexes. The reactions covered include hydrogenation, hydroformylation, carbonylation, Heck reactions, Suzuki and Stille couplings, Sonogashira reactions, allylic substitution, olefin metathesis, olefin epoxidation and alcohol oxidation.

Toward green catalytic synthesis—Transition metal-catalyzed reactions in non-conventional media

Two-dimensional nuclear magnetic resonance (NMR) relaxation time correlation measurements have been used to observe the behavior of liquids inside porous catalyst pellets; in particular, liquids of relevance to the hydrogenation of 2-butanone over a silica-supported ruthenium catalyst (Ru/SiO2). The behavior of 2-butanone is studied and compared to that of water and 2-propanol, which are used as solvents in this hydrogenation reaction. From the ratio of NMR relaxation times, T1/T2, for the liquids confined in the pores, it is possible to infer the relative strengths of the surface interaction for each liquid. Water is seen to have the strongest surface interaction, and 2-butanone has the weakest surface interaction. These results are supported by displacement experiments, in which one liquid replaces the other over time within the pore space of the catalyst. For comparison, the behavior of the same liquids in an alumina-supported palladium catalyst (Pd/Al2O3) was also studied. The variation in the strengt...

Comparing Strengths of Surface Interactions for Reactants and Solvents in Porous Catalysts Using Two-Dimensional NMR Relaxation Correlations

This paper overviews the development of the anthraquinone auto-oxidation (AO) process for the production of hydrogen peroxide in China and abroad. The characteristics and differences between the fixed-bed and fluidized-bed reactors for the AO process are presented. The detailed comparison indicates that the production of hydrogen peroxide with the fluidized-bed reactor has many advantages, such as lower operation cost and catalyst consumption, less anthraquinone degradation, higher catalyst utilization efficiency, and higher hydrogenation efficiency. The key characters of the production technology of hydrogen peroxide based on the fluidized-bed reactor developed by the Research Institute of Petroleum Processing, Sinopec are also disclosed. It is apparent that substituting the fluidized-bed reactor for the fixed-bed reactor is a major direction of breakthrough for the production technology of hydrogen peroxide in China.

Advances in the slurry reactor technology of the anthraquinone process for H 2 O 2 production

Spherical Al2O3 and SiO2–Al2O3 supports with different silica contents have been synthesized by the oil column method. After impregnation with Na2PdCl4 solution and subsequent calcination, PdO/Al2O3 and PdO/SiO2–Al2O3 catalyst precursors were obtained. X-ray powder diffraction and low temperature N2 adsorption–desorption measurements showed that the addition of silica increased the thermal stability, surface acidity, specific surface area and total pore volume of the spherical alumina. Temperature programmed reduction and H2–O2 titration indicated that Pd supported on the SiO2–Al2O3 spheres possessed higher dispersion and smaller particle size than that supported on pristine spherical Al2O3. Catalytic hydrogenation of ethylanthraquinone using molecular hydrogen was studied over the reduced Pd/Al2O3 and Pd/SiO2–Al2O3 catalysts with different silica contents. Under identical reaction conditions, the reaction activity and stability increased with increasing silica content.

Catalytic hydrogenation of ethylanthraquinone over highly dispersed eggshell Pd/SiO2-Al2O3 spherical catalysts

Advances in the production technology of hydrogen peroxide

The effect of water and NaOH was studied on the hydrogenation of 2-ethylanthraquinone (eAQ) over alumina supported 2% Pd/Al2O3-A and 12% Pd/Al2O3-B catalysts The hydrogenation was performed in a fixed-bed reactor by circulating the eAQ solution (the concentration of eAQ was 60 g/dm3) at 50 °C and 5 bar hydrogen pressure The egg-shell catalysts were prepared by the precipitation of palladium hydroxide onto the support A (activated alumina, preimpregnated with NaH2PO4) or support B (alumina containing 10% SiO2, and preimpregnated with Na2SiO3) Prior to the hydrogenation, the catalysts were dried and pre-treated with water vapour or NaOH solution The effect of water and NaOH on the amount of active quinones (eAQ and 2-ethyl-5,6,7,8-tetrahydroanthraquinone, H4eAQ) and in particular the role of such reagents in the consumption of aromatic hydroquinone eAQH2, the primary product of the quinone system of eAQ reduction was examined The saturation of the phenyl rings in eAQH2 produces H4eAQH2, which is a reactive compound and the hydrogenolysis of the C−O bond in the tautomerized eAQH2 leads to other degradation products Water and NaOH influence the hydrogenation of C O and the hydrogenolysis of C−O bond but have no effect on the hydrogenation of the aromatic rings The increase in activity in the former C O to C−OH reduction did not depend of alumina A and B as well as the type of reagent (NaH2PO4 or Na2SiO3) introduced to alumina during the catalyst preparation These reagents however, influenced the course of degradation processes Water when introduced to the catalyst exhibited unprofitable effect on maintenance the activity of catalyst during the hydrogenation run Such an unprofitable role is related to influence of water on the course of reactions yielding degradation products

2-Ethylanthraquinone hydrogenation on Pd/Al2O3 The effect of water and NaOH on the degradation process

The effects of the type of support and Pd concentration profile in alumina and silica supported egg-shell catalysts and their performance in the hydrogenation of 2-ethylanthraquinone (eAQ) were studied in 'Anthra' (AQ) and 'All-Tetra' systems. The activity and deactivation of catalysts were determined in the fixed-bed reactor. Solution saturated with hydrogen, (concentration of active quinones 60g/dm3, eAQ in the AQ system, 30% of eAQ and 70% of H4eAQ–2-ethlytetrahydroanthraquinone, in the All-Tetra system) was circulated through the catalyst bed at temperature 50°C and pressure 5bar. The contents of eAQ, active quinones, H4eAQ and degradation products were determined in the course of hydrogenation by GC method. The egg-shell palladium catalysts (1–2wt% Pd) prepared by the precipitation of palladium hydroxide onto alumina and silica supports pre-impregnated with various alkaline (NaHCO3, NaH2PO4, Na2SiO3) solutions were used in the hydrogenation experiments. Pd concentration profile inside the grains of catalysts was characterized by scanning electron microscopy. A difference between alumina and silica carriers with respect to the course of side reactions producing degradation products was found. Degradation of quinones in the hydrogenolytic reactions predominated on alumina supported catalysts, while the catalysts with silica favoured the hydrogenation of aromatic rings resulting in H4eAQ-active quinone. As a crucial factor for the decrease in the activity during the hydrogenation run, the reactivity of catalyst in the hydrogenolytic reactions was established. Alumina supported catalysts exhibited much higher deactivation than those of silica supported ones. Silica carrier as well as silica species introduced onto alumina under pre-impregnation with Na2SiO3 exhibited an advantageous role in the catalyst performance, in terms of activity and deactivation.

Hydrogenation of 2-Ethylanthraquinone over Pd/SiO2 and Pd/Al2O3 in the Fixed-Bed Reactor. The Effect of the Type of Support

Hydrogenation of 2-ethylanthraquinone (eAQ) in the fixed-bed reactor was studied in the “Anthra” (AQ) and “All-Tetra” systems on egg-shell palladium profile catalysts (0.7–2 wt.% Pd). Alumina modified with Na 2 SiO 3 solution was used as a support. Solution of active quinones (eAQ and 2-ethyltetrahydroanthraquinone H 4 eAQ) was saturated with hydrogen and circulated through the catalyst bed at the temperature 50 °C and the pressure 5 bar. The concentrations of eAQ, H 4 eAQ and degradation product were analysed by the GC method. Modification of the starting support with Na 2 SiO 3 was performed with three Sh, Lg and Vc procedures differing in the method of support drying and the time of support contacting with the Na 2 SiO 3 solution. Efficiency of modification was studied by specific surface area, porosity and Pd concentration profile. Procedure of support modification did not influence appreciably the rate of the main reaction eAQ to eAQH 2 reduction, while evidently affected the course of side reactions consuming desirable eAQH 2 and producing H 4 eAQ and degradation products. Performance of the catalysts in terms of their ability towards hydrogenolytic reactions producing degradation products and decrease in the activity during the hydrogenation run have been correlated with the efficiency of support modification with Si species. The better this efficiency, as in Vc procedure, the better maintenance of catalysts activity during the hydrogenation experiment.

R. Kangas

Papers

2-Ethylanthraquinone hydrogenation on Pd/Al2O3 The effect of water and NaOH on the degradation process

Hydrogenation of 2-Ethylanthraquinone over Pd/SiO2 and Pd/Al2O3 in the Fixed-Bed Reactor. The Effect of the Type of Support

Hydrogenation of 2-ethylanthraquinone on alumina-supported palladium catalysts: The effect of support modification with Na2SiO3