Catalytic wet air oxidation of stearic acid on cerium oxide supported noble metal catalysts

Catalytic wet air oxidation (CWAO) of stearic acid was carried out in a batch reactor over noble metals (Ru, Pd, Pt, Ir) catalysts supported on ceria. The influence of reaction conditions such as temperature, oxygen pressure and stearic acid concentration were investigated. The reaction occurs via a complex mechanism. The molecule of stearic acid can be oxidized by successive carboxy–decarboxylation (R_nCOOH + O₂ → R_n−1COOH +CO₂) yielding essentially CO₂ (route A). It may also be oxidized after CC bond rupture within the alkyl chain, which gives rise to significant amounts of acetic acid besides CO₂ (route B). Pt/CeO₂ is a very active catalyst in the conversion of stearic acid and extremely selective to carbon dioxide (route A), while the mechanism via CC bond splitting is much more marked on Ru/CeO₂. The catalyst characterization indicates that both noble metal and CeO₂ particles remain stable during the reaction.     

Catalytic decomposition of nitrous oxide over perovskite type solid oxide solutions and supported noble metal catalysts

The catalytic decomposition of nitrous oxide to nitrogen and oxygen has been investigated over various solid oxide solutions (SOS), La_0.8Sr_0.2MO_3– (M=Cr, Fe, Mn, Co or Y), La_1.8Sr_0.2CuO_4– and supported Pd, Pt catalysts. The reaction was carried out in a gradientless recycle reactor at 1 atm pressure with a feed gas containing about 0.5% N₂O (in helium). Among the various solid solutions, La_0.8Sr_0.2CoO_3– showed a maximum N₂O conversion of 90% at 600C. The order of activity observed for N₂O decomposition was La_0.8Sr_0.2CoO_3–>La_0.8Sr_0.2FeO_3–>La_1.8Sr_0.2CuO_4–> La_0.8Sr_0.2MnO_3–La_0.8Sr_0.2CrO_3–La_0.8Sr_0.2YO_3–. The activity of La_0.8Sr_0.2CoO_3– was compared with supported Pd, Pt and also with unsubstituted LaCoO₃ catalysts under similar reaction conditions. Among all the catalysts tested in this study, Pd/Al₂O₃ showed the lowest light-off temperature for N₂O decomposition. The activity of La_0.8Sr_0.2CoO_3– was found to be comparable to Pd/Al₂O₃ catalyst at temperatures above 500 C. The influence of added oxygen (about 4%) in the feed was examined over La_0.8Sr_0.2CoO_3– and Pd/Al₂O₃ catalysts and only in the case of cobalt catalyst was the conversion of N₂O decreased by 13%. By choosing varied sintering conditions, La_0.8Sr_0.2CoO_3– of different BET surface areas were prepared and the light-off temperature was found to decrease with increase in surface area. The results obtained over solid solutions are discussed on the basis of the cation mixed valency and oxygen properties of the catalyst.     

Catalytic combustion of benzene over supported metal oxides catalysts

Catalytic combustion of benzene over supported metal oxides has been investigated. The catalysts have been prepared by incipient wetness method and characterized by XRD, FT-Raman, ESR and TPR. Among supported metal oxides, CuO_x, supported on TiO₂ is found to have the highest activity for benzene oxidation. In addition, among the catalysts of copper oxide supported on TiO₂, A1₂O₃ and SiO₂, titania-supported catalyst (CuO_x/TiO₂) gives the highest catalytic activity. CuO_x/TiO₂ (Cu loading 5.5 wt%) shows the total oxidation of benzene at about 250 °C. From the ESR and FT-Raman results, the CuO dispersed on the TiO₂ surface acts as an active site of CuO_x/TiO₂ catalysts on the oxidative decomposition of benzene. The catalytic activity gradually increases with an increase of Cu loading on TiO₂. When Cu loading reaches 5.5 wt%, the total conversion temperature is lowered to 300 °C. However, the catalytic activity considerably decreases at 7 wt% Cu loading. The catalytic activity increased with an increase of oxygen concentration but the concentration of benzene showed no difference in the benzene conversion. This result suggests that the rate determining step is the adsorption of oxygen.     

Catalytic oxidation of trichloroethylene over TiO2 supported ruthenium catalysts

Different types of TiO₂ (anatase, P25 and rutile) supported ruthenium catalysts were synthesized by wet impregnation and directly reduced in H₂. The distribution characteristics of ruthenium species were thoroughly studied before and after trichloroethylene oxidation. The results show that ruthenium oxide species are very unstable in the anatase phase, but quite stable in the rutile phase of TiO₂. This phenomenon results in different catalytic behaviors for the Ru/TiO₂ catalysts. The Ru/TiO₂ (P25) catalyst has the best catalytic performance among these catalysts. The complete conversion temperature of trichloroethylene is in the temperature range of 260–270 °C.     

Dibenzothiophene hydrodesulfurization by noble metal supported catalysts

The hydrodesulfurization of dibenzothiophene (DBT) is investigated at 240°C, under one atmosphere pressure of H₂ + DBT, in a DBT conversion range giving rise to a H₂S concentration between 30 and 200 ppm. The turnover number (TN) of platinum slightly decreases as the dispersion of platinum (Ptins) to Pt ratio = D (Pt)) increases from 0.01 to 0.7, whatever support (α-Al₂0₃, SiO₂, chlorinated γ-Al₂O₃, SiO₂-Al₂O₃, montmorillonite) was used. Furthermore, the TN is much lower for highly dispersed Pt/γ-Al₂O₃-C1 (D(Pt) = 0.9; ø (Pt) = 1.0 nm). Pt/TiO₂ (D(Pt) = 0.06 or D(Pt) = 0.34) reduced or re-reduced at 240°C has a higher TN than the preceding catalysts. Reduction or re-reduction of Pt/TiO₂, at 500°C results in only a relatively small decrease in the catalytic activity, in spite of the appearance of a strong metal-support interaction observed by several workers. For different supported metals on Al₂O₃, the TN follows the sequence: Pt > Ir > Ru > Re. Alloying Ir or Ru (25 to 30 at %) with Platinum results in a relatively small decrease in the TN (per one (Pt_s + Ir_s or Ru_s ) atom).The activity, per unit weight of catalyst, of an industrial Co-Mo/γ-Al₂O₃ sulfided catalyst (HR 306) is equivalent to that of 1 % Pt/γ-Al₃0₃ (D(Pt) = 0.7). The present platinum supported catalysts have a very low selectivity in hydrogenation (production of phenylcyclohexane, PCH < 1 %), except when supported by silica, SiO₂-Al₂O₃ or montmorillonite; the Co-Mo/γ-Al₂0₃ catalyst has a selectivity which is intermediate between Pt/γ-Al₂O₃ and Pt/SiO₂-Al₂O₃ or montmorillonite. The deactivation (decrease in activity versus the time en-stream) is lower for Co-Moγ-Al₃0₃ than for Pt/γ-Al₃O₃, but the addition of Ge to Pt/γ-Al₂O₃ gives rise to a more stable catalyst.     

Catalytic wet air oxidation of acetic acid over different ruthenium catalysts

Ruthenium catalysts were prepared by impregnation of different supports: ZrO₂, CeO₂, TiO₂, ZrO₂–CeO₂ and TiO₂–CeO₂. Their activities for acetic acid oxidation in aqueous solution were investigated in a stirred reactor at a reaction temperature of 200 °C and total pressure of 4 MPa. The order of the catalyst activity obtained was RuO₂/ZrO₂–CeO₂ > RuO₂/CeO₂ > RuO₂/TiO₂–CeO₂ > RuO₂/ZrO₂ > RuO₂/TiO₂, which corresponds to surface concentration of non-lattice oxygen (defect-oxide or hydroxyl-like group) of these catalysts. The non-lattice oxygen on the catalyst surface plays an important role in the catalytic activity.     

Direct conversion of triglycerides to olefins and paraffins over noble metal supported catalysts

Deoxygenation of methyl esters and triglycerides was studied for production of either α-olefins or diesel components. The reactions were carried out in a reactive distillation fashion in which products are quickly removed from the reaction mixture in flowing He. The effects of He flow rate, reaction temperature, active component and support were studied. PtSnK supported on silica was found to be the best catalyst for selective production of α-olefins. Palm kernel oil and coconut oil were also deoxygenated to produce α-olefins or diesel components, depending on reaction conditions.     

Complete oxidation of 2-propanol over gold-based catalysts supported on metal oxides

This paper concerns the preparation of metal oxide-supported gold catalysts and their application to 2-propanol abatement in order to lower the light off temperature. Catalytic oxidation of 2-propanol was investigated on Au/CeO₂, Au/Fe₂O₃, Au/TiO₂ and Au/Al₂O₃ catalysts prepared from the deposition–precipitation (DP) method. The catalysts are characterized by XRD (X-ray diffraction), BET (Brunner–Emmett–Teller), TEM (transmission electron microscopy), NH₃-TPD (NH₃-temperature programmed desorption), H₂-TPR (H₂-temperature programmed reduction), ICP-AES (inductively coupled plasma-atomic emission spectroscopy) and XPS (X-ray photoelectron spectroscopy) techniques. The catalytic activity of Au/metal oxide samples towards the deep oxidation of 2-propanol to CO₂ and water has been found to be strongly dependent on the kind of supports, the amount of gold loading, the calcination temperature and the moisture content in the feed.     

Hydrotreatment of jatropha oil over noble metal catalysts

Jatropha oil is a promising nonedible feedstock for producing renewable diesel. In this work, the hydrotreatment processing of jatropha oil was investigated. Instead of using conventional alumina-supported Co–Mo, Ni–Mo, and Ni–W catalysts that need sulfidation pretreatment, noble metals such as Pd and Ru were chosen. Trials were performed in an isothermal trickle-bed reactor and the reaction conditions were as follows: temperature 603–663?K, weight hourly space velocity (WHSV) 1 to 4/h, pressure 1.5–3?MPa, and H₂/oil ratio 200–800 (v/v). Yield of n-C₁₅ to n-C₁₈ hydrocarbons was maximized (70.3 and 43.8% for Pd/Al₂O₃ and Ru/Al₂O₃, respectively) at the following conditions: T?=?663 K, WHSV?=?2/h, P?=?3?MPa, and H₂/oil ratio?=?600 (v/v). Since Ru favored cracking reactions to a larger extent than Pd, the yield of C₁₅ to C₁₈ hydrocarbons over Ru/Al₂O₃ was lowered. Using simple first-order plots for oil conversion, activation energies for the hydrotreating process over Pd/Al₂O₃ and Ru/Al₂O₃ were found and they were equal to 109 and 121?kJ/mol, correspondingly.     

Catalytic decomposition of N2O over monolithic supported noble metal-transition metal oxides

The decomposition of nitrous oxide to nitrogen and oxygen using a series of monolithic (ceria-alumina washcoated cordierite) supported transition metal (Cu, Fe, Co, Ni, Mn) and noble metal (Ir, Rh) oxide catalysts has been studied using gas chromatography. The effect of combining a transition metal with a noble metal has also been investigated. A synergetic effect was observed between transition metal and noble metal oxides in the presence of a small amount of water for some of the catalysts. The synergy between Fe-Ir and Ni-Ir was also verified under dry conditions. X-ray photoelectron spectroscopic measurements on these catalysts indicate that Fe, Rh and Ir are present predominantly as Fe₂O_3, RhO₂ and IrO₂, while significant amounts of Co and Ni ions may migrate inside the support to form cobalt and nickel aluminate. Only the Fe-Ir catalyst showed a significant interaction between the noble metal and the transition metal. The effect of water, oxygen and carbon monoxide on the catalytic behaviour of the five most active catalysts (Ni-Ir, Ni-Rh, Fe-Ir, Co-Ir, Ir) has also been investigated. Oxygen and water were found to inhibit the catalytic activity, although the extent of oxygen inhibition is limited, presumably due to the presence of ceria in the monolith washcoat support. Conversely, carbon monoxide greatly enhances catalytic activity.     

催化湿式氧化中负载型催化剂制备

采用浸渍法制备了负载型催化剂CuO/γ-Al_2O_3和Fe_2O_3/γ—Al_2O_3,以甲基橙为代表化合物,考察了制备因素对催化活性的影响,结果表明,CuO/γ-Al_2O_3的活性高于Fe_2O_3/γ-Al_2O_3,催化湿式氧化甲基橙2 h,脱色率接近100%。正交试验和稳定性研究表明,焙烧温度对催化活性影响较大,350℃焙烧,催化剂活性组分Cu溶出较少,且重复使用情况较好。采用SEM和XRD等手段对CuO/γ-Al_2O_3进行表征,发现其活性组分分散度良好。     

Carbon xerogel supported noble metal catalysts for fine chemical applications

Carbon xerogels are mesoporous materials obtained upon pyrolysis of the dried gels resulting from polycondensation of resorcinol and formaldehyde. Treatment with nitric acid under severe conditions introduces high amounts of oxygen containing functional groups onto the surface of the material, leading however to the collapse of its porous structure. The resulting material is then used to support 1 wt.% Pt, Ir and Ru monometallic catalysts by wet impregnation using organometallic precursors. The catalysts are characterized by N₂ adsorption–desorption isotherms at 77 K, temperature programmed desorption coupled with mass spectrometry, scanning and transmission electron microscopy, and H₂ chemisorption. The liquid-phase selective hydrogenation of cinnamaldehyde to cinnamyl alcohol is used in order to assess the catalytic performance of the prepared materials. Pt and Ru catalysts are initially very selective towards the hydrogenation of the olefinic double bond, while Ir is mostly selective towards the carbonyl group. After a thermal post-reduction treatment at 973 K, selectivity towards cinnamyl alcohol is significantly improved regardless of the metal nature. The Pt catalyst exhibits the best behavior, a complete shift in C=C to C=O hydrogenation being detected. The improvement in selectivity is rationalized in terms of both an increase in metal particle size and a modification in the surface chemistry of the catalyst after the post-reduction treatment.     

Production of hydrogen for fuel cells by steam reforming of ethanol over supported noble metal catalysts

The catalytic performance of supported noble metal catalysts for the steam reforming (SR) of ethanol has been investigated in the temperature range of 600–850 °C with respect to the nature of the active metallic phase (Rh, Ru, Pt, Pd), the nature of the support (Al₂O₃, MgO, TiO₂) and the metal loading (0–5 wt.%). It is found that for low-loaded catalysts, Rh is significantly more active and selective toward hydrogen formation compared to Ru, Pt and Pd, which show a similar behavior. The catalytic performance of Rh and, particularly, Ru is significantly improved with increasing metal loading, leading to higher ethanol conversions and hydrogen selectivities at given reaction temperatures. The catalytic activity and selectivity of high-loaded Ru catalysts is comparable to that of Rh and, therefore, ruthenium was further investigated as a less costly alternative. It was found that, under certain reaction conditions, the 5% Ru/Al₂O₃ catalyst is able to completely convert ethanol with selectivities toward hydrogen above 95%, the only byproduct being methane. Long-term tests conducted under severe conditions showed that the catalyst is acceptably stable and could be a good candidate for the production of hydrogen by steam reforming of ethanol for fuel cell applications.     

Preferential CO oxidation over supported Pt catalysts

Preferential CO oxidation reaction has been carried out at a gas hourly space velocity of 46,129 h^?1 over supported Pt catalysts prepared by an incipient wetness impregnation method. Al2O3, MgO-Al₂O₃ (MgO=30 wt% and 70 wt%) and MgO were employed as supports for the target reaction. 1 wt% Pt/Al₂O₃ catalyst exhibited very high performance (X _CO >90% at 175 ^°C for 100 h) in the reformate gases containing CO₂ under severe conditions. This result is mainly due to the highest Pt dispersion, easier reducibility of PtO _x , and easier electron transfer of metallic Pt. In addition, 1 wt% Pt/Al₂O₃ catalyst was also tested in the reformate gases with both CO₂ and H₂O to evaluate under realistic condition.     

NO oxidation over supported cobalt oxide catalysts

NO oxidation was conducted over cobalt oxides supported on various supports such as SiO₂, ZrO₂, TiO₂, and CeO₂. The N₂ physisorption, an inductively coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray diffraction (XRD), NO chemisorptions, the temperature-programmed desorption (TPD) with a mass spectroscopy after NO or CO chemisorptions were conducted to characterize catalysts. Among tested catalysts, Co₃O₄ supported on ceria with a high surface area showed the highest catalytic activity. This catalyst showed superior catalytic activity to unsupported Co₃O₄ with a high surface area and 1 wt% Pt/γ-Al₂O₃. For ceria-supported Co₃O₄, the catalytic activity, the NO uptake at 298 K and the dispersion of Co₃O₄ increased with increasing the surface area of CeO₂. The active participation of the lattice oxygen in NO oxidation could not be observed. On the other hand, the lattice oxygen participated in the CO oxidation over the same catalyst. The deactivation was observed over Co₃O₄/CeO₂ and 1 wt% Pt/γ-Al₂O₃ in the presence of SO₂ in a feed. 1 wt% Pt/γ-Al₂O₃ was deactivated by SO₂ more rapidly compared with Co₃O₄/CeO₂.     

Catalytic wet air oxidation of aqueous solution of 2-chlorophenol over Ru/zirconia catalysts

Ru loaded zirconia catalysts (Ru/ZrO₂) were found to be active in the catalytic wet air oxidation (CWAO) of 2-chlorophenol (2-CP) at relatively mild temperature. To optimize the reaction conditions, the effects of different operating parameters, such as the rotation speed, the reaction temperature, the total pressure, the initial concentration and the pH of the initial 2-CP solution on the catalytic activity of 3 wt.% Ru/ZrO₂ were evaluated. The activation energy for the CWAO of 2-CP over Ru/ZrO₂ was calculated to be 36 kJ mol⁻¹. The 2-CP removal rate is zero order with respect to the initial 2-CP concentration. The CWAO of 2-CP changes from first order (oxygen diffusion control) to zero order (kinetic control) with respect to the oxygen partial pressure when the total pressure is higher than 4 MPa. The conversion of 2-CP increases with the pH of the initial 2-CP solution. The dechlorination reaction is promoted at higher pH. However, too high pH limits the total mineralization of 2-CP because the adsorption of the reaction intermediates is hindered. It was also confirmed that Ru(NO)(NO₃)₃ is better than RuCl₃ to act as a ruthenium precursor.     

Hydrodeoxygenation of dibenzofuran over noble metal supported on mesoporous zeolite

Hydrodeoxygenation has been considered to be one of the most promising methods for bio-oil upgrading. In this paper, the catalytic performance of noble metal supported on mesoporous zeolite in model bio-oil compound hydrodeoxygenation was examined. Dibenzofuran was chosen here because of its refractory nature and large molecular size. Our results indicate that Pt supported on mesoporous ZSM-5 show better performance in dibenzofuran hydrodeoxygenation than Pt/ZSM-5 and Pt/Al₂O₃. The excellent catalytic performance is attributed to the combination of strong acidity and mesopore structure in mesoporous zeolite.     

负载型金属催化剂催化KBH4水解析氢性能研究

以高比表面积和规整性强的蜂窝陶瓷（2MgO₂·Al₂O₃·SiO₂）为载体，涂敷TiO₂后，用水热合成法分别负载铁、钴和镍盐，500 ℃焙烧及硼氢化钾（KBH₄）浸渍后，合成了负载型金属催化剂。负载不同金属盐的催化剂析氢性能比较结果为钴＞铁＞镍。实验研究表明，负载硝酸铁［Fe(NO₃)₃·9H₂O］和氯化钴(CoCl₂·6H₂O)的催化剂经KHB₄浸渍后析氢性能均明显改善。利用X射线衍射（XRD）和X射线光电子能谱（XPS）对催化剂的表征结果证实,负载硝酸铁催化剂表面真正起催化析氢性能的活性组分为单质铁，负载氯化钴催化剂表面生成了CoTiO₃，且该催化剂具有优良的催化碱性KBH₄溶液水解析氢性能，常温下该催化剂0.34 g于NaOH质量分数约为18%，KBH4质量分数约为10%的溶液中催化析氢速率可达160 mL·min^－1。