Hydrodechlorinative dimerization of 1,1,1-trifluorohaloethanes over Ru/SiO2 catalyst

The hydrodechlorination of CCl₃-CF₃ (CFC-113a) was studied over silica-supported metal catalysts. Pd/SiO₂ and Pt/SiO₂ catalysts showed high activity for the replacement reaction of the chlorine atoms in CFC-113a with hydrogen. On the other hand, Ru/SiO₂ selectively catalyzed the dimerization and gave CF₃-CC1=CC1-CF₃ and CF₃-CCl₂-CC1₂-CF₃. CHC1₂-CF₃ (HCFC-123) and CC1₂F-CF₃ (CFC-114a) also dimerized into the corresponding C₄-dimers over the catalyst. The reactivity of CF₃-having haloethanes on the Ru/SiO₂ decreased in the order of CFC-113a > HCFC-123 > CFC-114aHCFC-124. The selectivity of dimerization decreased with decreasing the reactivity of substrates.     

Effect of Ag addition on the properties of Pd–Ag/TiO2 catalysts containing different TiO2 crystalline phases

Anatase and rutile TiO₂ were used for preparation of the TiO₂ supported Pd and Pd–Ag catalysts for selective hydrogenation of acetylene. It was found that Pd/TiO₂-anatase exhibited higher acetylene conversion and ethylene selectivity than rutile TiO₂ supported ones. However, addition of Ag to Pd/TiO₂-anatase catalyst resulted in lower ethylene selectivity while that of Pd/TiO₂-rutile increased. It is suggested that Ag addition suppressed the beneficial effect of the Ti³⁺ sites presented on the anatase TiO₂ during selective acetylene hydrogenation whereas without Ti³⁺, Ag promoted ethylene selectivity by blocking sites for over-hydrogenation of ethylene to ethane.     

Development of High-Efficiency,Magnetically Separable Palladium-Decorated Manganese-Ferrite Catalyst for Nitrobenzene Hydrogenation

Aniline (AN) is one of the most important compounds in the chemical industry and is prepared by the catalytic hydrogenation of nitrobenzene (NB). The development of novel, multifunctional catalysts which are easily recoverable from the reaction mixture is, therefore, of paramount importance. Compared to conventional filtration, magnetic separation is favored because it is cheaper and more facile. For satisfying these requirements, we developed manganese ferrite (MnFe₂O₄)–supported, magnetically separable palladium catalysts with high catalytic activity in the hydrogenation of nitrobenzene to aniline. In addition to high NB conversion and AN yield, remarkable aniline selectivity (above 96 n/n%) was achieved. Surprisingly, the magnetic support alone also shows moderate catalytic activity even without noble metals, and thus, up to 94 n/n% nitrobenzene conversion, along with 47 n/n% aniline yield, are attainable. After adding palladium nanoparticles to the support, the combined catalytic activity of the two nanomaterials yielded a fast, efficient, and highly selective catalyst. During the test of the Pd/MnFe₂O₄ catalyst in NB hydrogenation, no by-products were detected, and consequently, above 96 n/n% aniline yield and 96 n/n% selectivity were achieved. The activity of the Pd/MnFe₂O₄ catalyst was not particularly sensitive to the hydrogenation temperature, and reuse tests indicate its applicability in at least four cycles without regeneration. The remarkable catalytic activity and other favorable properties can make our catalyst potentially applicable to both NB hydrogenation and other similar or slightly different reactions.     

CFC-12催化加氢制备HFC-32的研究

探索了二氟二氯甲烷(CFC-12)催化加氢制备HFC-32的方法.比较了不同贵金属催化剂及催化剂载体对加氢反应的影响,结果表明Pd/C催化剂对CFC-12的转化率和HFC-32的选择性都要优于其它的催化剂.研究了助剂Th对Pd/C催化剂性能的影响,发现添加一定量的Th可有效改善HFC-32的选择性,但过多的Th将导致CFC-12转化率的下降.该法为实现CFC-12无害化处理提供了一条可行的途径.     

Comparison of homogeneous and heterogeneous palladium hydrogenation catalysts

Mechanistic and kinetic studies of Pd-catalyzed hydrogenation at atmospheric pressure and 30–100 C were carried out with methyl sorbate, methyl linoleate and conjugated linoleate. Homogeneous Pd catalysts and particularly Pd-acetylacetonate [Pd(acac)₂] were significantly more selective than Pd/C in the hydrogenation of sorbate to hexanoates, mainlytrans-2-hexenoate. Relative rate constants for the different parallel and consecutive reactions, determined by computer simulation, indicated that the low diene selectivity of Pd/C can be dattributed to a significant direct reduction of sorbate to hexanoate. The similar behavior of PdCl₂ to that of Pd/C suggests that Pd(II) was initially reduced to Pd(O). Valence stabilization of PbCl₂ by adding DMF or a mixture of Ph₃P and SnCl₂ increased the diene selectivity but decreased the activity. Stabilization of Pd(acac)₂ with triethylaluminum (Ziegler catalyst) resulted in increased activity but decreased selectivity. The kinetics of methyl linoleate hydrogenation showed that although Pd(acac)₂ was only half as active as Pd/C, their respective diene selectivity was similar (10.4 and 9.6). The much greater reactivity of conjugated compared with unconjugated linoleate toward Pd(acac)₂ suggests the possible formation of conjugated dienes as intermediates that are rapidly reduced and not detected in the lipid phase during hydrogenation.     

Hydroisomerization of model FCC naphtha over sulfided Co(Ni)–Mo(W)/MCM-41 catalysts

Deep hydrodesulfurization (HDS) of gasoline generally brings about the saturation of olefins and leads to the serious octane number losses. Conversion of linear olefins to branched ones followed by hydrogenation to isoalkanes would minimize such octane number losses. In this work, MCM-41-supported Co–Mo, Ni–Mo and Ni–W catalysts were prepared by the incipient wetness impregnation method, and compared with an industrial Co–Mo/γ-Al₂O₃ catalyst. The surface acidities were measured by the techniques of microcalorimetry and infrared spectroscopy for the adsorption of ammonia, and probed by the reaction of conversion of isopropanol. The isomerization and hydrogenation of 1-hexene as well as the HDS of thiophene were studied by using model FCC naphtha. It was found that the sulfidation enhanced significantly the surface Brønsted acidity that favored the skeletal isomerization of 1-hexene under the HDS conditions. Since the isomerization and hydrogenation of 1-hexene are the two competition reactions, the catalysts with relatively lower hydrogenation activity may have higher selectivity to the isomerization reactions. The Co–Mo/MCM-41 showed the high selectivity to the skeletal isomerization reactions due to its strong surface Brønsted acidity and the relatively low hydrogenation activity. On the other hand, the Ni–Mo/MCM-41 exhibited high hydrogenation activity and therefore low selectivity to the isomerization reactions although it possessed quite strong surface Brønsted acidity. The Ni–W/MCM-41 exhibited the low activity for the HDS of thiophene and isomerization of 1-hexene due to the poor dispersion of active metals.     

Pd nanoparticles supported on ZIF-8 as an efficient heterogeneous catalyst for the selective hydrogenation of cinnamaldehyde

Palladium nanoparticles supported on ZIF-8 (Pd/ZIF-8) were prepared by a facile impregnation method and characterized by XRD, TEM, ICP and N₂ adsorption. The prepared Pd/ZIF-8 catalyst exhibited excellent catalytic performance for the selective hydrogenation of cinnamaldehyde. The reaction solvents had great influences on the catalytic performance of the prepared Pd/ZIF-8 catalyst. Pd nanoparticles supported on ZIF-8 gave much higher catalytic activity and hydrocinnamaldehyde selectivity than those supported on other MOFs or the conventional inorganic supports. The prepared Pd/ZIF-8 catalyst could be reused at least four times without significant loss in activity and selectivity.     

Hydrogenation of Nitrobenzene with Supported Transition Metal Catalysts in Supercritical Carbon Dioxide

Transition metal catalysts such as Pd, Pt, Ru, and Rh supported on carbon, silica and alumina have been examined for the hydrogenation of nitrobenzene (NB) in supercritical carbon dioxide (scCO₂) and in ethanol. The order of hydrogenation activity is Pt>Pd>Ru, Rh in scCO₂ and in ethanol. The effectiveness of the support is C>Al₂O₃, SiO₂ for either Pt or Pd in scCO₂. For all the catalysts, higher selectivity to aniline has been obtained in scCO₂ compared with ethanol. Hydrogenation of nitrobenzene catalyzed with Pd/C and Pt/C catalysts was successfully conducted in scCO₂ with a 100% yield to aniline at a lower reaction temperature of 35 °C. The product aniline (organic phase) can be easily separated from the side‐product water (aqueous phase), solvent (scCO₂), and catalyst (solid) by a simple phase separation process. The hydrogenation of NB is a structure‐sensitive reaction in ethanol as well as in scCO₂ except for a few Pt/C catalysts in which the degree of metal dispersion is small (<0.08).     

Upgrading of Lignin-Derived Compounds: Reactions of Eugenol Catalyzed by HY Zeolite and by Pt/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Abstract  

The conversion of eugenol (4-allyl-2-methoxyphenol), a compound derived from the lignin in woody biomass, was catalyzed by HY zeolite at 573 K and atmospheric pressure. The main products were isoeugenol and guaiacol, formed by isomerization and by deallylation, respectively. Substituted guaiacols with saturated side-chains (4-methylguaiacol, 4-ethylguaiacol, and 4-propylguaiacol) were also formed, by hydrogen transfer and alkylation reactions. The pseudo-first-order rate constant for the overall disappearance of eugenol was found to be 12.4 L (g of catalyst)/h. When the catalyst was Pt/γ-Al₂O₃ used in the presence of H₂, significant hydrogenation of the propenyl side-chain took place, accompanied by isomerization, and hydrodeoxygenation. Under similar operating conditions, the reaction catalyzed by Pt/γ-Al₂O₃ in the presence of H₂ gave a higher eugenol conversion (X = 0.70) than the reaction catalyzed by HY zeolite (X = 0.11), primarily because of the dominant hydrogenation observed with the former catalyst. In the absence of H₂ as a co-reactant, the acidic γ-Al₂O₃ support in Pt/γ-Al₂O₃ evidently catalyzed all the classes of reactions catalyzed by HY zeolite.     

Selectivity controlling in the hydrogenation of 1,3-butadiene on Tl-modified Pd catalyst

The selectivity and reactivity in the hydrogenation of 1,3-butadiene catalyzed by Tl-modified 5 wt% Pd/Al₂O₃ catalysts vary with amounts of Tl loading and with the reduction temperatures, that is, the main product was 1-butene and trans-2-butene for values of Tl loading of 0.5 and 2 in Tl/Pd atomic ratio, respectively, when the catalysts were reduced at 673 K. 1,3-butadiene was hydrogenated selectively towards 1-butene and trans-2-butene when the Tl modified 5 wt% Pd/Al₂O₃ catalyst of Tl/Pd = 2 was reduced at 300 and 373 K or above, respectively. On the catalyst with Tl/Pd = 2 reduced at 373 K or above, the butenes formed are not hydrogenated to butane, even after a long reaction time. These results suggest the formation of Pd-Tl alloy or intermetallic compounds during the reduction procedure which is responsible for the selectivity controlling in the reaction. TPR and XRD results were in consistence with the reaction data.     

Pd catalysed hexyne hydrogenation modified by Bi and by Pb

Two Pd/Al₂O₃ catalysts of different loadings and dispersions were modified by the addition of various amounts of Bi and studied in the hydrogenation of 1-hexyne and 2-hexyne and in the consecutive reactions of the products formed. Catalyst behaviour was compared with a commercial Lindlar catalyst and Pb-free Pd/CaCO₃. Results are consistent with a preference of Bi to occupy step and edge sites while leaving the terraces and extended facets relatively unaffected. Results show that while Bi had little effect on the rate of the 1-hexyne hydrogenation, the rate of subsequent reactions of the 1-hexene formed were suppressed. In this context, Bi was a more effective modifier than Pb. This situation was reversed when reactions were performed using 2-hexyne. Results are discussed in terms of the reaction mechanism and key intermediates in the process and the roles of bismuth, relative to lead, in creating an appropriate ensemble of surface Pd atoms to permit control of selectivity.     

Promotional SMSI Effect on Supported Palladium Catalysts for Methanol Synthesis

High-temperature reduction (HTR) of palladium catalysts supported on some reducible oxides, such as Pd/CeO₂, and Pd/TiO₂ catalysts, led to a strong metal-support interaction (SMSI), which was found to be the main reason for their high and stable activity for methanol synthesis from hydrogenation of carbon dioxide. But low-temperature-reduced (LTR) catalysts exhibited high methane selectivity and were oxidized to PdO quickly in the same reaction. Besides palladium, platinum exhibited similar behavior for this reaction when supported on these reducible oxides. Mechanistic studies of the Pd/CeO₂ catalyst clarified the promotional role of the SMSI effect, and the spillover effect on the HTR Pd/CeO₂ catalyst. Carbon dioxide was decomposed on Ce₂O₃, which was attached to Pd, to form CO and surface oxygen species. The carbon monoxide formed was hydrogenated to methanol successively on the palladium surface while the surface oxygen species was hydrogenated to water by spillover hydrogen from the gas phase. A reaction model for the hydrogenation of carbon dioxide was suggested for both HTR and LTR Pd/CeO₂ catalysts. Methanol synthesis from syngas on the LTR or HTR Pd/CeO₂ catalysts was also conducted. Both alcohol and hydrocarbons were formed significantly on the HTR catalyst from syngas while methanol formed predominantly on the LTR catalyst. Characterization of these two catalysts elucidated the reaction performances.     

Methanol synthesis over Pd/SiO2 with narrow Pd size distribution prepared by using MCM-41 as a support precursor

All silicious MCM-41 was investigated as a support or a support precursor for Pd/SiO₂ and prepared catalysts were tested for methanol synthesis from CO and H₂. The methods of Pd loading on the MCM-41 were impregnation, seed impregnation and chemical vapor deposition (CVD). For both impregnations, most Pd existed outside of the pore as large particles, and only a small part of Pd was inserted into the pore of MCM-41 retaining the initial structure. On the contrary, in the catalyst prepared by CVD method, the MCM-41 structure was completely destroyed to become amorphous SiO₂. Yet the average Pd particle size in this catalyst was smaller and its distribution was narrower than those of the catalysts prepared by impregnation methods. In the methanol synthesis from CO hydrogenation the catalyst prepared by CVD showed higher methanol selectivity than other MCM-41-derived catalysts. This result was considered to be due to the more uniform distribution of the Pd particle size.     

Gas-phase hydrogenation of maleic anhydride to butyric acid over Cu/TiO2/γ-Al2O3 catalyst promoted by Pd

The promoter effect of palladium on the Cu/TiO₂/γ-Al₂O₃ catalyst was investigated for the gas-phase selective hydrogenation of maleic anhydride to butyric acid at atmospheric pressure. The results show that Pd is added rarely into the Cu/TiO₂/γ-Al₂O₃ catalyst for the hydrogenation of maleic anhydride, the higher selectivity to butyric acid can be obtained. In the absence of Pd (or Cu) in the Cu–Pd/TiO₂/γ-Al₂O₃ catalyst, the selectivity to butyric acid (BA) is nearly zero. Using the Cu–Pd/TiO₂/γ-Al₂O₃ (Pd/Cu=3/100 (atom)) catalyst, 56.2% selectivity to BA and 100% conversion of maleic anhydride were obtained at 280 °C.     

Effect of catalyst deactivation on mild hydrocracking reactions

A WNiPd/TiO₂Al₂O₃ mild hydrocracking catalyst deactivation has been studied in a small pilot plant unit. OTMHCK technology can produce low sulfur, high cetane number diesel at constant conversion with acceptable cycle length by increasing initial temperature as a function of time on stream. Three sets of tests were performed for 3 months at constant operating temperature using the same catalyst. At the start and at the end of the run the catalyst activity and selectivity were tested at different temperatures. Spent catalyst was characterized using chemical analysis, ¹³C NMR, XPS, and ammonia adsorption techniques. The hydrocracking reactions were modeled using a lump model including 63-equation reactions, an empirical reactivity function and three distribution functions that included hydrogenation, cracking, and ring opening in liquid phase. Deactivation reaction was simulated using a Levenspiel's two sites type of deactivation mechanism. A Genetic Algorithm tool was used to obtain the deactivation constant using a set of previously determined kinetic constants. This set takes into account the aromatics adsorption on metal and acid sites. The results confirm that deactivation changes the relative rate of hydrogenation/hydrogenolysis, cracking and dealkylation reactions.     

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

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.     

The electrochemical hydrogenation of edible oils in a solid polymer electrolyte reactor. II. Hydrogenation selectivity studies

Soybean oil has been hydrogenated electrochemically in a solid polymer electrolyte (SPE) reactor at 60°C and 1 atm pressure. These experiments focused on identifying cathode designs and reactor operation conditions that improved fatty acid hydrogenation selectivities. Increasing oil mass transfer into and out of the Pd-black cathode catalyst layer (by increasing the porosity of the cathode carbon paper/cloth backing material, increasing the oil feed flow rate, and inserting a turbulence promoter into the oil feed flow channel) decreased the concentrations of stearic acid and linolenic acid in oil products [for example, an iodine value (IV) 98 oil contained 12.2% C_18:0 and 2.3% C_18:3]. When a second metal (Ni, Cd, Zn, Pb, Cr, Fe, Ag, Cu, or Co) was electrodeposited on a Pd-black powder cathode, substantial increases in the linolenate, linoleate, and oleate selectivities were observed. For example, a Pd/Co cathode was used to synthesize an IV 113 soybean oil with 5.3% stearic acid and 2.3% linolenic acid. The trans isomer content of soybean oil products was in the range of 6–9.5% (corresponding to specific isomerization indices of 0.15–0.40, depending on the product IV) and did not increase significantly for high fatty acid hydrogenation selectivity conditions.     

Palladium and platinum catalysts supported on carbon nanofiber coated monoliths for low-temperature combustion of BTX

In this work carbon nanofiber (CNF)-coated monoliths with a very thin, homogeneous, consistent and good adhered CNF layer were obtained by means of catalytic decomposition of ethylene on Ni particles.The catalytic behaviour of Pt and Pd supported on the CNF-coated monoliths was studied in the low-temperature catalytic combustion of benzene, toluene and m-xylene (BTX) and compared with the performance of Pt and Pd supported on γ-Al₂O₃ coated monoliths.The catalysts supported on CNF-coated monoliths were the most active, independent of the metal catalyst or the type of the tested aromatic compound. TPD experiments showed that the γ-Al₂O₃ phase retained important amounts of the water molecules produced during the reaction. When water vapour was supplied to the reactant flow, the activity of Pd catalysts decreased much stronger than the Pt ones, and the activity of the Pt catalysts supported on the γ-Al₂O₃ was more affected than that of the catalysts supported on CNF.BTX combustion reactions seem to be catalyzed by Pt and Pd through different kinetic mechanisms, explaining why Pt catalysts always were more active than the Pd ones deposited on the same type of support. Pd catalyzed combustion of benzene is strongly inhibited by oxygen and by water.Catalysts supported on CNF-coated monoliths showed a selectivity to burn benzene better than toluene or m-xylene, attributed to a better aromatic-CNF surface interaction.     

Pd/polyaniline(SiO2) a novel catalyst for the hydrogenation of 2-ethylanthraquinone

A novel palladium catalyst supported on silica grains coated with polyaniline (PANI) (24.4 wt% of polymer) was used for the hydrogenation of 2-ethylanthraquinone (eAQ). This 2%Pd/PANI(SiO₂) catalyst exhibited much better selectivity in the hydrogenation of eAQ to active quinones than that of 2%Pd/SiO₂ prepared by a conventional precipitation method. It is suggested that the modification of properties of Pd centres by PANI matrix, has an effect on their reactivity. The weakening of the strength of hydrogen bonding and hydrophobic character of polymer both can be considered as factors remarkably improving performance of Pd/PANI(SiO₂) catalyst.     

Deactivation and coke formation on palladium and platinum catalysts in vegetable oil hydrogenation

Deactivation of palladium and platinum catalysts due to coke formation was studied during hydrogenation of methyl esters of sunflower oil. The supported metal catalysts were prepared by impregnating γ-alumina with either palladium or platinum salts, and by impregnating α-alumina with palladium salt. The catalysts were reused for several batch experiments. The Pd/γ-Al₂O₃ catalyst lost more than 50% of its initial activity after four batch experiments, while the other catalysts did not deactivate. Samples of used catalysts were cleaned from remaining oil by repeated extractions with methanol, and the amount of coke formed on the catalysts was studied by temperature-programmed oxidation. The deactivation of the catalyst is a function of both the metal and the support. The amount of coke increased on the Pd/γ-Al₂O₃ catalyst with repeated use, but the amount of coke remained approximately constant for the Pt/γ-Al₂O₃ catalyst. Virtually no coke was detected on the Pd/α-Al₂O₃ catalyst. The formation of coke on Pd/α-Al₂O₃ may be slower than on the Pd/γ-Al₂O₃ owing to the carrier’s smaller surface area and less acidic character. The absence of deactivation for the Pt/γ-Al₂O₃ catalyst may be explained by slower formation of coke precursors on platinum compared to palladium.