The highly dispersed supported ruthenium-yttrium (Ru-Y) bimetallic catalysts were prepared by impregnation method and their catalytic performance for hydrogenation of ester was fully investigated. The catalyst was characterized by X-ray diffraction and field emission scanning electron microscopy. The results show that the average particle diameter of the bimetallic crystallites was less than 10 nm. The effects of the reaction temperature, the hydrogen pressure, the amount of catalyst and the proportion of yttrium in catalyst on the hydrogenation of ester were studied. The experimental results show that the introduction of yttrium not only changed the chemical and textural properties of ruthenium-based catalyst but also controlled the formation of Ru-Y alloy. The Ru-Y catalyst (Ru-2%Y/TiO 2) exhibited high catalytic activity and good selectivity towards the higher alcohols. Under optimal reaction conditions of 240°C and 5 MPa hydrogen pressure, the conversion of palm oil esters was above 93.4% while the selectivity towards alcohol was above 99.0%.
Fatty alcohols (FAlcs) and their derivatives are widely used as surfactants, lubricants, solvents, synthetic detergents, antifoaming agents, perfumes, cosmetics and pharmaceuticals, and as additives in many industrial products [
Since the last century, the natural-fatty-alcohol-based surfactants have gained growing significance in the detergent market due to their excellent washing properties and superior biodegradability. Therefore, the hydrogenation of FAME to the corresponding FAlcs is of great industrial importance. And the concern of catalyst research is raised because catalyst is the key technology for the effective production of FAlcs and the successful utilization of natural FAME. Many efforts have been made to develop high active catalysts [
During the last decade, the development of biodiesel has been emphasized. Biodiesel is defined as a fatty acid methyl ester obtained by the trans-esterification route of renewable biological sources with methanol. It can offer abundant feedstock for the hydrogenation to obtain FAlcs. Therefore, the research subject is to focus on improving the selectivity and yield of FALcs to the highest possible. It is reported that depositing the amorphous alloys on support [
RuCl3 (Sinopharm Chemical Reagent Co., Ltd., >99.6%), Y(NO3)3 (Sinopharm Chemical Reagent Co., Ltd., >99.9%), Methyl palmitate (Aladdin Reagent Co. Ltd., >99.9%), TiO2 (100 - 160 mero), hydrogen (99.99%) and the other reagents were used as received.
All the catalysts were prepared by the impregnation method in aqueous suspensions. The metallic precursors (such as ruthenium chloride and yttrium nitrate) were dissolved in deionic water. Then, the titania was impregnated with above solution for overnight. And water was employed by evaporation at 333 K for 5 h. Next, the samples were dried at 393 K for 12 h. The solids were subjected to calcination treatment for 4 h at 673 K under air flow and reduced by hydrogen for 3 h at 453 K.
In order to eliminate the surface acidity of the catalyst, the catalyst was treated with barium nitrate and washed with deionic water until the absence of barium cations. The solids were dried for 6 h under vacuum. For the bimetallic catalysts, with moninal concentration of 5 wt% in Ru and 2.5 wt% in Y was employed, designated as 5% Ru - 2.5% Y/TiO2.
The powder XRD patterns were recorded at room temperature on a Philips X’ Pert Pro MPD X-ray diffraction with Cu-Kα radiation at 50 kV and 35 mA. The 2θ angles were scanned from 15˚ to 75˚ at a rate of 0.1(˚)/s. High-resolution TEM (HRTEM) images were obtained on a Philips TECNAIF-30 FEG instrument at an accelerating voltage of 300 V. The sample was dispersed with dry ethanol.
The reaction was performed in a 60 mL stainless autoclave with a glass linear and magnetic stirrer. A typical procedure for hydrogenation of methyl palmitate (Scheme 1) is as follows: the appropriate amounts of palm oil esters, catalyst and cyclehexane were directly introduced into the autoclave, followed by a purge with hydrogen several times. Hydrogen was introduced until the desired hydrogen pressure was reached. The reaction was carried out under the designed conditions for a desired time. After the reaction, the autoclave was quickly cooled in a water bath and vented. The liquid products were separated from the reaction mixture by decantation and analyzed by GC 4002A (SUPELCOWAXTM10 0.25 mm × 0.25 μm × 30 m ), incorporating an FID detector. The solid residue obtained was reused in the next reaction.
In order to further identify the crystalline phase of Ru in the catalyst, power X-ray diffraction patterns of the six solids with different metal loadings were obtained, as shown in
To evaluate the catalytic activity of Ru-Y/TiO2, the hydrogenation of methyl palmitate was chosen as a probing reaction. In all the runs, the selectivity for 1-hexadecanol in the products was more than 99%, only trace amounts of by-products palmitic acid were detected by GC-MS.
In order to investigate the effect of the amount of Y in catalyst on the hydrogenation, several kinds of catalysts with different amount of Y were used in the hydrogenation of methyl palmitate. It is clear from
Scheme 1. Hydrogenation of methyl palmitate.
The amount of yttrium % | 0 | 0.5 | 1 | 1.5 | 2 | 5* |
---|---|---|---|---|---|---|
Conversion (%) | 10.4 | 29.3 | 72.5 | 75.8 | 93.4 | 0 |
Reaction conditions: catalyst 30 mg, methyl palmitate 1.85 mmol, cyclohexane 1 mL, 220˚C, 5 MPa, 10 h. *The supported catalyst was Y/TiO2.
Y doping amount is 0.5%, the conversion rate is just 29.3%. However, when Y doping amount is 2%, the conversion rate reached up to 93.4%. The doping of rare earth metals is one of the efficient methods to improve the activity of supported metal catalysts. This is probably due to the 4f electrons in Y electronic structure. Its outermost electronic structure is 4f 1+n5d0-16s2. Most of the earth metals have no 5d electron, so they could easily lose two 6s electrons, one d electron or f electron to form trivalent cations whose outermost electron configuration is 4fn5s26p2. From the electronic structure, the 5d orbital is empty, which provides a good electron transferring orbital and could be used as an electron transferring station with catalytic action. With the increasing of Y doping amounts, Y scrambles for electrons to reduce the composite of electron hole pair on TiO2 surface so that more O2− or O2−OH are generated on the catalyst surface which has higher catalytic activity. Meanwhile, the specific electronic structure and larger radius of earth metals lead to lattice expansion on Ru/TiO2 surface, which is beneficial to the generation of catalytic active center, increasing of catalytic active center numbers and improving of adsorption capacity of catalysts to hydrogen so as to increase conversion rates.
The effect of temperature on the catalytic activity is shown in
Under the same conditions, the effect of the hydrogen pressure on the hydrogenation reaction of methyl palmitate was studied by altering the hydrogen pressure. When using 1.85 mmol methyl palmitate, 30 mg catalyst and 1 mL cyclohexane at 220˚C for 10 h, the results are listed in
To investigate the stability of catalyst, the reaction mixture was separated from the catalyst by decantation after the reaction and analyzed by GC. The catalyst was directly reused for the next run. The results of hydrogenation are shown in
The supported ruthenium-yttrium bimetallic catalysts were prepared by impregnation and their catalytic performances for hydrogenation of ester were evaluated. The XRD and TEM results reveal that the active metals are highly dispersed and the alloy is formed by Ru with Y. The catalytic results indicate that the catalytic activity of Ru-Y/TiO2 depends on the loading of yttrium. The ruthenium-yttrium catalyst (Ru-2%Y/TiO2) exhibits high catalytic activity and good selectivity towards the higher alcohols compared with Ru/TiO2 and Y/TiO2. Furthermore, the catalyst can be easily separated from the organic products and reused for seven times without significant decrease of activity and selectivity.
This work was supported financially by the Great Science & Technology Research Program from Fujian Province
Temp. (˚C) | 180 | 200 | 220 | 230 | 240 | 250 |
---|---|---|---|---|---|---|
Conversion (%) | 3.9 | 7.5 | 23.2 | 29.3 | 50.3 | 65.7 |
Reaction conditions: catalyst 25 mg, methyl palmitate 1.85 mmol, cyclohexane 1 mL, 5 MPa, 10 h.
PH2 (MPa) | 3 | 4 | 5 | 6 | 7 |
---|---|---|---|---|---|
Conversion (%) | 38.0 | 56.2 | 72.5 | 74.8 | 78.2 |
Reaction conditions: catalyst 25 mg, methyl palmitate 1.85 mmol, cyclohexane 1 mL, 220˚C, 10 h
Cycle | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
---|---|---|---|---|---|---|---|
Conversion (%) | 43.1 | 44.5 | 47.4 | 49.3 | 56.9 | 52.1 | 50.6 |
Reaction conditions: catalyst 25 mg, methyl palmitate 1.85 mmol, cyclohexane 1 mL, 5 MPa, 6 h, 240˚C.
of China (Project No. 2011H6021), the Nature Science Foundation of Fujian Province of China (Project No. 2013J01053), the Science & Technology Research Program from Education Office of Fujian Province (Project No. JA12268) and the Science & Technology Research Program of Fuzhou Municipal, China (Project No. 2012-G-128).