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Applied Catalysis A, General (v.293, #)
Suitable catalysts for hydroisomerization of long-chain normal paraffins by H. Deldari (pp. 1-10).
Nowadays, isomerization of normal paraffins plays an important role in the petroleum industry. Isomerization reactions generally take place over bifunctional metal/acid catalysts. The suitable catalysts for hydroisomerization of long chain n-paraffins are reviewed in this paper. An ideal catalyst for this purpose should provide a high yield of isomerization and should have shape-selectivity to react only with n-paraffins. To achieve these characteristics, the catalyst should have suitable compositional and structural characteristics, mainly: proper balance between metal and acid sites, medium pore size, high dispersion of metal on surface of catalyst, mild acidity, and strength distribution of acid sites. Catalysts with mean pore size and low acidity that are loaded with noble metals, especially platinum, have very good performance in hydroisomerizations of long-chain normal paraffins.
Keywords: Hydroisomerization; Long-chain normal paraffins; Bifunctional catalyst; Metal function; Acid function
Reaction pathways on NiMo/Al2O3 catalysts for hydrodesulfurization of diesel fuel by Narinobu Kagami; Bas M. Vogelaar; A. Dick van Langeveld; Jacob A. Moulijn (pp. 11-23).
The ranking of catalytic activities of several NiMo catalysts was performed using various model compounds: thiophene (TH), tetrahydrothiophene (ThTH), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). So-called type I and type II NiMo catalysts were prepared by varying Mo loading from below to above monolayer coverage. Type I and II differ most at high loading. Below monolayer surface coverage, type II active phase shows higher HG activity than type I. It is likely that type II active phase consists of higher stacking active phases, favoring the HG pathway. Consequently, type II catalyst shows higher HDS activity for TH and 4,6-DMDBT, as these sulfur compounds react mainly via HG pathway. Above monolayer surface coverage, type I active phase forms aggregated crystals on the support alumina, resulting in a low dispersion, whereas type II active phase can maintain high dispersion. Higher loading type I catalyst shows lower DDS activity and only slightly increased HG activity. Higher loading type II phase shows higher DDS and extremely high hydrogenation (HG) activity and, as a consequence, high HDS activity for TH and 4,6-DMDBT.In order to be able to generalize the results, we included a CoMo catalyst in the study. The results at first sight are not fully consistent. Although this catalyst shows a low HG activity in HDS of DBT, it shows a relatively high activity in HDS of 4,6-DMDBT. Two reaction schemes were examined, one of them taking into account a dehydrogenation step. Although a dehydrogenation step could occur under our experimental conditions, the main cause of ranking differences is the differences of susceptibility for NiMo and CoMo catalysts to H2S.
Keywords: NiMo/Al; 2; O; 3; CoMo/Al; 2; O; 3; Hydrotreating; Hydrodesulfurization; Reaction pathways; Thiophene; Dibenzothiophene; 4,6-Dimethyldibenzothiophene
Spatially resolved in situ measurements of transient species breakthrough during cyclic, low-temperature regeneration of a monolithic Pt/K/Al2O3 NO x storage-reduction catalyst by Jae-Soon Choi; William P. Partridge; C. Stuart Daw (pp. 24-40).
We employed a new experimental technique known as spatially resolved capillary-inlet mass spectrometry (SpaciMS) to observe the evolution of multiple species inside the channels of a monolithic NO x storage-reduction (NSR) catalyst. The NSR material consisted of a Pt/K/Al2O3 washcoat deposited inside cordierite monolith channels. Spatially and temporally resolved measurements were made over the monolith length in a bench flow reactor during fast cycling between synthetic lean and rich environments at 200 and 300°C. Regeneration was found to be very efficient at 300°C regardless of whether pure H2, pure CO, or mixtures of H2 and CO were employed. At 200°C, CO was noticeably less effective than H2. We conjecture that at 200°C CO may be inhibiting the regeneration process through its strong adsorption on Pt. Generation of H2 by water-gas shift was seen at 300°C but not at 200°C.
Keywords: NO; x; storage-reduction; Lean NO; x; trap; Pt/K/Al; 2; O; 3; Monolith; Regeneration; Spatially resolved speciation; SpaciMS; Water-gas shift reaction
Styrene oxide transformation on SiO2-stabilised Ag nanoparticles prepared by gamma-radiolysis by A. Sárkány; I. Sajó; P. Hargittai; Z. Papp; E. Tombácz (pp. 41-48).
Ag nanoparticles have been prepared by gamma-radiolysis of AgNO3 in aqueous matrix of SiO2 (Aerosil 200) in the presence of 2-propanol as OH radical scavenger. The presence of SiO2 prevents rapid agglomeration of Ag and the Ag nanoparticles formed become attached to SiO2. Transmission electron microscope (TEM), XRD and UV–vis measurements have shown that by adjusting the SiO2/solvent ratio the size of Ag nanoparticles can be controlled. Decreasing solvent/SiO2 ratio and high dose rate facilitated formation of small particles of 2–6nm on SiO2. The in situ generation of Ag particles on silica has been attributed to the participation of solvated electrons formed at the silica/solvent interfacial layer. The Ag/SiO2 catalysts were tested in transformation of styrene oxide in hydrogen/He stream. The main reaction pathway is removal of oxygen. The low yield of aldehyde and alcohol can be attributed to low surface coverage of hydrogen on Ag.
Keywords: Ag nanoparticles; Gamma-irradiation; UV–vis; TEM; Catalysis; Styrene oxide hydrogenation
MCM41 and silica supported MoVTe mixed oxide catalysts for direct oxidation of propane to acrolein by Luqian Chen; Jun Liang; Hong Lin; Weizheng Weng; Huilin Wan; Jacques. C. Védrine (pp. 49-55).
Bulk Mo1.3V0.3Te0.3 mixed oxide and MCM41 and amorphous silica supported Mo1.3V0.3Te0.3 mixed oxide (3 and 8mol%, i.e. 6 and 15% monolayer coverage on MCM41 and 19 and 51% monolayer coverage on silica, respectively) catalysts have been synthesized and studied for direct oxidation of propane (DOP) to acrolein (ACR). After calcination at 853K for 2h under flowing nitrogen, characterization results (XRD, Raman and TEM-EDX) show that Mo species, MoV, MoTe and VTe mixed oxides with various compositions are present in the samples before and after testing, but after testing the EDX analyses indicate more domains rich in Mo when using a narrow electron beam (Ø∼5–10nm in size), particularly for bulk and 8mol% supported samples. At variance, broad electron beam (Ø∼50–100nm in size) EDX analyses give values close to chemical compositions. This shows that under catalytic conditions, solid-state reaction has occurred leading to restructuring of several phases present in the samples, with extraction of some volatile MoO3. Catalytic study at reaction temperature 773K shows that amorphous silica and MCM41 supports exhibit catalytic activity in DOP to ACR, respectively. This means that homogeneous reaction occurs in the gas phase under the studied conditions after initiation on the solid surface. Mo1.3V0.3Te0.3 mixed oxide is shown to be highly dispersed on MCM41 and silica supports, particularly for low mixed oxide content (3mol%) leading to higher selectivity and yield in ACR obtained than that for bulk samples, in particular for MCM41 support. This is indicated to arise from a better dispersion of the active phases, which favors redox properties of the catalytic materials and prevents deep oxidation of propane.
Keywords: Bulk Mo; 1.3; V; 0.3; Te; 0.3; mixed oxide catalysts; Silica; MCM41; Supported Mo; 1.3; V; 0.3; Te; 0.3; mixed oxide catalysts; Propane direct oxidation; Acrolein
129Xe NMR analysis of sulfided Co-Mo/Al2O3 catalyst by Kazuhiko Hagiwara; Takeshi Ebihara; Nobuaki Urasato; Takashi Fujikawa (pp. 56-63).
We investigated an application of129Xe NMR to the analysis of sulfided Co-Mo/Al2O3 catalysts. For a mixture of Mo/Al2O3 and Co/Al2O3, two signals appeared in the129Xe NMR spectrum, while only one signal appeared in the spectrum of other catalysts such as Mo/Al2O3 and Co-Mo/Al2O3. The downfield signal was attributed to Mo/Al2O3 and the other one was attributed to Co/Al2O3. This result demonstrates that xenon atoms adsorbed on Mo/Al2O3 make few exchanges with ones adsorbed on Co/Al2O3 in the mixture during the NMR measurement. For sulfided Co-Mo/Al2O3, the chemical shift δ of the signal varied nonlinearly against the amount of adsorbed xenon, N. This suggests that the electrons of xenon strongly interacts with coordinative unsaturated sites at the edges of the stacked MoS2 crystallite. Furthermore, we calculated the term δ0 that is mainly dependent on collisions between xenon and other atoms by fitting the δ curve against N to the theoretical equation. δ0 became gradually larger with the increasing Co/Mo ratio and reached its maximum value at Co/Mo=0.71. This behavior is mainly caused by a growth of the term δM that is dependent on the magnetic susceptibility. Such results suggest the formation of the Co–Mo–S phase, indicating the antiferromagnetism. On the other hand, δ0 slightly decreased at Co/Mo=0.99. This is closely related with the formation of not only the Co–Mo–S phase but also Co9S8, indicating the diamagnetism. Hence, δ0 is a parameter that represents the formation of the Co–Mo–S phase, and129Xe NMR can be a powerful tool for analysis of the Co–Mo–S phase on Co-Mo/Al2O3 hydrodesulfurization catalysts.
Keywords: 129; Xe NMR analysis; Cobalt molybdenum catalyst; Co–Mo–S phase; Magnetic susceptibility; Hydrodesulfurization
Cu2O as active species in the steam reforming of methanol by CuO/ZrO2 catalysts by Hisayuki Oguchi; Hiroyoshi Kanai; Kazunori Utani; Yasuyuki Matsumura; Seiichiro Imamura (pp. 64-70).
Steam reforming of methanol (SRM) was carried out at 250°C over CuO/CeO2 and CuO/ZrO2 catalysts with various CuO contents and water/MeOH ratios in a flow reaction system. The 80wt.% CuO/ZrO2 gave the highest activity, and the optimum water/MeOH ratio was 1.5. The oxidation states of Cu species in post-reaction catalyst depended upon CuO contents and the water/MeOH ratio. The starting copper compounds were CuO in all cases, and the copper in almost all catalysts was reduced to metallic Cu. Cu2O appeared in 80 and 90wt.% CuO/ZrO2 when water/MeOH ratios were above 1 irrespective of reducing atmospheres. The reduction behavior of the 80wt.% CuO/ZrO2 catalyst with hydrogen was investigated by XANES technique in an in situ cell. In the narrow temperature range of 180–200°C, CuO was reduced to metallic Cu via the intermediate Cu2O. The Fourier transform magnitude of K-edge Zr of 80wt.% CuO/ZrO2 showed that the configuration of zirconium in the catalysts was very similar to that of monoclinic zirconia. The Debye rings of 80wt.% CuO/ZrO2 and 80wt.% CuO/CeO2 catalysts showed that zirconia was less coagulated at 300°C than CeO2; heat resistance of ZrO2 is higher than that of CeO2. BET surface area of 80wt.% CuO/ZrO2 was 85.3m2/g, and that of 80wt.% CuO/CeO2 was 46.0m2/g, suggesting that ZrO2 in the catalyst has micro crystallites and is highly dispersed.
Keywords: Steam reforming of methanol; H; 2; production; Cu; 2; O; CuO/ZrO; 2; XRD; XANES
Autothermal reforming of n-octane on Ru-based catalysts by Aidu Qi; Shudong Wang; Guizhi Fu; Diyong Wu (pp. 71-82).
In an attempt to effectively integrate catalytic partial oxidation (CPO) and steam reforming (SR) reactions on the same catalyst, autothermal reforming (ATR) of n-octane was addressed based on thermodynamic analysis and carried out on a non-pyrophoric catalyst 0.3wt.% Ru/K2O-CeO2/γ-Al2O3. The ATR of n-octane was more efficient at the molar ratio of O2/C 0.35–0.45 and H2O/C 1.6–2.2 (independent parameters), respectively, and reforming temperature of 750–800°C (dependent parameter). Among the sophisticated reaction network, the main reaction thread was deducted as: long-chain hydrocarbon→CH4, short-chain hydrocarbon→CO2, CO and H2 formation by steam reforming, although the parallel CPO, decomposition and reverse water gas shift reaction took place on the same catalyst. Low temperature and high steam partial pressure had more positive effect on CH4 SR to produce CO2 other than CO. This was verified by the tendency of the outlet reformate to the equilibrium at different operation conditions. Furthermore, the loss of active components and the formation of stable but less active components in the catalyst in the harsh ATR atmosphere firstly make the CO inhibition capability suffer, then eventually aggravated the ATR performance, which was verified by the characterizations of X-ray fluorescence, BET specific surface areas and temperature programmed reduction.
Keywords: Hydrogen; Autothermal reforming; Noble metal catalyst; Fuel processor; PEMFC; Distributed power system
Catalytic activities and surface properties of zeolite-supported molybdenum nitrides for NO reduction with H2 by C. Shi; A.M. Zhu; X.F. Yang; C.T. Au (pp. 83-90).
A series of zeolite (H-ZSM-5)-supported molybdenum nitride catalysts with Mo loading ranging from 2 to 30wt.% were synthesized by temperature-programmed nitridation in a flow of NH3. The surface properties of the nitride samples were characterized by XPS, H2-TPR, and XRD techniques and their catalytic activities were evaluated for NO reduction with H2. For the fresh samples, molybdenum nitrides coexisted with oxides on the zeolite. With the increase of Mo loading from 2 to 30wt.%, the degree of nitridation increased linearly with the increase of Mo loading. We observed that a catalyst with higher Mo loading exhibited higher initial activities. The nitrided 2wt.% Mo/H-ZSM-5 catalyst was the most stable and NO conversion to N2 remained unchanged within a test period of 15h. For the catalysts with Mo loading above 2wt.%, catalytic activities decreased with time on stream. After 15h, the nitrided 2wt.% Mo/H-ZSM-5 catalyst was the most active among the tested catalysts. The results of H2-TPR measurements for the used and oxygen-saturated catalysts revealed that catalyst deactivation was a result of oxygen incorporation into the nitride lattices. The strong interaction between the molybdenum species and H-ZSM-5 zeolite as well as the lowering of H2-reduction temperature of surface oxygen might be the reasons for the good performance of the nitrided 2wt.% Mo/H-ZSM-5 catalyst for NO reduction with H2.
Keywords: H-ZSM-5 zeolite; Molybdenum nitride; NO reduction
Determination of dispersion of precious metals on CeO2-containing supports by Tatsuya Takeguchi; Shunsuke Manabe; Ryuji Kikuchi; Koichi Eguchi; Takaaki Kanazawa; Shinichi Matsumoto; Wataru Ueda (pp. 91-96).
Precious metal (PM) dispersions on CeO2-containing supports were examined. When dispersions were evaluated by the H2–O2 titration method, the CeO2-containing supports hide the true redox of PM because of the large oxygen storage-reduction capacity of the oxide, resulting in higher apparent dispersions than the exact values. When Pt dispersions on the CeO2 support were evaluated by the ordinary CO pulse method, CO was adsorbed on the CeO2 support as carbonate species accompanying the oxidation with lattice oxygen. Therefore, the dispersions estimated from the CO uptake were also higher than the exact value. Infrared spectra also clearly evidenced the presence of carbonate species after CO adsorption. To prevent the CO adsorption on CeO2 as the carbonate species, we treated Pt/CeO2 with CO2 before CO adsorption. The strong bands arising from carbonate species on CeO2 were observed in the infrared spectra. When CO was adsorbed on CO2-terated Pt/CeO2, CO was selectively adsorbed on the surface atoms of Pt particles. By the O2–CO2–H2–CO pulse method, the amount of CO adsorbed on surface atoms of the Pt particles could be separated, and a precise dispersion was determined.
Keywords: Pt/CeO; 2; Pt/CeO; 2; –ZrO; 2; CO adsorption; CO; 2; treatment
Epoxidation using non-heme iron complexes in solution and immobilized on silica gel as catalysts by Clovis Piovezan; Kelly Aparecida Dias Freitas de Castro; Sueli Maria Drechsel; Shirley Nakagaki (pp. 97-104).
The epoxidation of the carbon–carbon double bound by metallocomplexes is systematically investigated using metallomacrocycles like metalloporphyrins as heme models for cytochrome P-450. Herein, we report the synthesis and characterization of a new complex [Fe2(bbppnol)(μ-AcO)(H2O)2](ClO4)2 (A), a non-heme metallocomplex, as well as its catalytic activity in olefin oxidation. The bis(aquo) complexA and [Fe2(bbppnol)(μ-AcO)2](PF6) (B) (previously prepared) were also immobilized on silica gel, and the obtained heterogeneous catalysts were characterized. The catalytic activity of such solid materials in the oxidation of cyclooctene and cyclohexene was investigated using iodosylbenzene and H2O2 as oxidants. The obtained results were compared with the catalytic behavior of the corresponding iron complexes in solution (homogeneous catalysis).
Keywords: Epoxidation; Catalysis; Hydroxylase; Binuclear iron complexes; Non-heme complexes
Activation of alumina-supported hydrotreating catalysts by organosulfides or H2S: Effect of the H2S partial pressure used during the activation process by Samuel Texier; Gilles Berhault; Guy Pérot; Fabrice Diehl (pp. 105-119).
The influence on the hydrodesulfurization (HDS) of dibenzothiophene (DBT) of different activation procedures using H2S or dimethyldisulfide (DMDS) has been investigated on phosphorus-free and phosphorus-doped CoMo and NiMo industrial catalysts supported on alumina. The comparison of the two sulfiding agents was performed using strictly similar procedures of sulfidation to determine the origin of the well-known beneficial effect of organosulfides for the activation of hydrotreating catalysts. Partial pressures in H2 and/or in sulfiding agents have been modified to observe activity variations among the different sulfiding agents used. Comparison between H2S and DMDS has also been performed on phosphorus-doped CoMoP/Al2O3 and NiMoP/Al2O3 catalysts.Results emphasized the importance of supplying H2S to the catalyst at low temperatures of activation (around 423K) even in a low proportion (PH2S as low as 3.3kPa) to sulfide correctly NiMo and CoMo catalysts. Indeed, through a low consumption of H2S, O–S exchange and intramolecular redox reactions can be initiated at low temperatures of activation leading to a level of sulfidation sufficiently advanced before reaching temperatures (above 573K) at which a strong competition between reduction and sulfidation starts. DMDS appears less efficient than H2S for activating NiMo and CoMo catalyst due to its inability to provide H2S to the catalyst at these low temperatures of activation. At higher temperatures ( T>543K), a good activation cannot be obtained if a highPH2/PH2S ratio is used whatever the sulfiding agent. Finally, the difficulty of activating the P-doped CoMoP/Al2O3 and NiMoP/Al2O3 catalysts was confirmed.This study confirms that the beneficial role of organosulfide compounds as activating agents is not related to a pure “chemical� phenomenon but more probably to a “thermal well� effect limiting the exothermic character of the oxide–sulfide transformation.
Keywords: Activation; Hydrodesulfurization; Sulfidation; Dimethyldisulfide; MoS; 2; Phosphorus doping
Molybdate-exchanged layered double hydroxides for the catalytic disproportionation of hydrogen peroxide into singlet oxygen: Evaluation and improvements of1O2 generation by combined chemiluminescence and trapping experiments by Joos Wahlen; Dirk E. De Vos; Bert F. Sels; Véronique Nardello; Jean-Marie Aubry; Paul L. Alsters; Pierre A. Jacobs (pp. 120-128).
The generation of singlet molecular oxygen (1O2) from H2O2 catalyzed by molybdate-exchanged layered double hydroxides (Mo-LDHs) was studied by chemiluminescence (CL) and chemical trapping (CT) experiments. In the first part, the utility of chemiluminescence spectroscopy to quantify the amount of1O2 produced in heterogeneous media was evaluated by comparison with1O2 yields determined in homogeneous solutions of sodium molybdate. On the other hand, the1O2 yields determined by CL spectroscopy were compared with those obtained via chemical trapping of1O2 with β-citronellol as an olefinic substrate. Advantages and limitations of CL spectroscopy for the determination of1O2 yields in heterogeneous media are discussed. CL spectroscopy allows the rapid screening of heterogeneous catalysts for the generation of1O2. On the other hand, the spectroscopic technique only yields the total amount of1O2 and provides no information on the availability of the produced1O2 for reaction with olefinic substrates. In the second part, CL and CT experiments were used to determine optimized conditions for the generation of1O2 from Mo-LDHs. Compositional parameters of the catalyst and reaction conditions were varied. A Mo-LDH catalyst possessing a low Mg/Al molar ratio and a low Mo loading was identified as the optimum catalyst in terms of activity and efficiency. Methanol and N, N-dimethylformamide are the optimum solvents.
Keywords: Chemiluminescence spectroscopy; Heterogeneous catalysis; Hydrogen peroxide; Hydroperoxides; Layered double hydroxide (LDH); Molybdate; Oxidation; Singlet oxygen
High-pressure catalytic combustion of gasified biomass in a hybrid combustor by J.C.G. Andrae; D. Johansson; M. Bursell; R. Fakhrai; J. Jayasuriya; A. Manrique Carrera (pp. 129-136).
Catalytic combustion of synthetic gasified biomass was conducted in a high-pressure facility at pressures ranging from 5 to 16bars. The catalytic combustor design considered was a hybrid monolith (400cpsi, diameter 3.5cm, length 3.6cm and every other channel coated). The active phase consisted of 1wt.% Pt/γ-Al2O3 with wash coat loading of total monolith 15wt.%. In the interpretation of the experiments, a two-dimensional boundary layer model was applied successfully to model a single channel of the monolith. At constant inlet velocity to the monolith the combustion efficiency decreased with increasing pressure. A multi-step surface mechanism predicted that the flux of carbon dioxide and water from the surface increased with pressure. However, as the pressure (i.e. the Reynolds number) was increased, unreacted gas near the center of the channel penetrated significantly longer into the channel compared to lower pressures. For the conditions studied ( λ=4–6, Tin=218–257°C and residence time ∼5ms), conversion of hydrogen and carbon monoxide were diffusion limited after ignition, while methane never ignited and was kinetically controlled. According to the kinetic model surface coverage of major species changed from CO, H and CO2 before ignition to O, OH, CO2 and free surface sites after ignition. The model predicted further that for constant mass flow combustion efficiency increased with pressure, and was more pronounced at lower pressures (2.5–10bar) than at higher pressures (>10bar).
Keywords: Catalytic combustion; Gasified biomass; Platinum; High pressure; Catalytically stabilized combustion; CHEMKIN
Effect of the coexistence of nitrogen compounds on the sulfur tolerance and catalytic activity of Pd and Pt monometallic catalysts supported on high-silica USY zeolite and amorphous silica by Takashi Matsui; Masaru Harada; Makoto Toba; Yuji Yoshimura (pp. 137-144).
The effects of coexistence of nitrogen compounds on the catalytic activity of the Pd and Pt monometallic catalysts supported on amorphous silica and high-silica USY zeolite (SiO2/Al2O3=390) were investigated using a high-pressure fixed-bed continuous flow reactor operating at 3.9MPa and 553K. Types of catalytic activity studied included the tetralin hydrogenation activity and the 4,6-dimethyldibenzothiophene (4,6-DMDBT) hydrodesulfurization activity. The Pd/USY zeolite catalyst showed the highest tetralin hydrogenation activity with feedstock containing only 4,6-DMDBT ( S=300ppm) without nitrogen compounds. However, its hydrogenation activity was strongly inhibited by the addition of n-butylamine ( N=20ppm). Significant inhibitory effects by nitrogen compounds were also observed for the Pd/SiO2 catalyst. The Pt/USY zeolite catalyst showed lower hydrogenation activity than the Pd/USY zeolite, while the Pt/SiO2 catalyst showed higher activity than the Pd/SiO2 catalysts. The inhibitory effects of nitrogen compounds on these Pt catalysts were less pronounced than on Pd catalysts. On the other hand, with respect to hydrodesulfurization, Pt catalysts showed higher activity in 4,6-DMDBT hydrodesulfurization than Pd catalysts, irrespective of the support species, due to the latter's higher hydrogenolytic ability to cleave the CS bond even in the presence of nitrogen compounds. On the other hand, Pd catalysts were subject to a decrease in 4,6-DMDBT hydrodesulfurization resulting from a loss in hydrogenation activity in the presence of nitrogen compounds. We conclude that Pt catalysts are superior to Pd catalysts with respect to both hydrogenation and hydrodesulfurization for the hydrotreatment of industrial feedstocks containing sulfur and nitrogen compounds.
Keywords: Pd; Pt; Noble metal catalyst; USY zeolite; Silica; Sulfur; Nitrogen; Tolerance; Poisoning; Tetralin; 4,6-Dimethyldibenzothiophene; Butylamine; Hydrogen sulfide; Ammonia; Hydrogenation; Hydrodesulfurization
Characterization of coke deposited on Pt/alumina catalyst during reforming of liquid hydrocarbons by Abolghasem Shamsi; John P. Baltrus; James J. Spivey (pp. 145-152).
Temperature-programmed oxidation (TPO), Raman spectrometry, and X-ray photoelectron spectroscopy (XPS) are used to characterize coke species deposited on a 0.61wt% Pt/alumina catalyst for three reactions, carried out separately: partial oxidation (POX), steam reforming (SR), and autothermal reforming (ATR). Three individual compounds were used as simulants of liquid fuels in each of these three reactions: tetradecane, decalin, and 1-methylnaphthalene. The TPO profiles of the coke showed that partial oxidation and steam reforming resulted in generally greater coke deposition than autothermal reforming for each of the fuels. 1-Methylnaphthalene produces more coke than the other fuels in each of the reactions. Coke appears to be deposited both on the metal and the support, with the coke on the metal being more easily oxidized by TPO.Raman spectroscopy shows that there is no significant change in the carbon crystallite size on any of the catalysts; all are within the range of 1.45–1.83nm. XPS analysis of carbon deposited during partial oxidation of tetradecane shows that small amounts of graphitic carbon (C/Al ratio<0.10) remain even after treatment in oxygen for 15min at 600°C.
Keywords: Catalyst; Reforming; Fuel processing; Carbon
Synthesis of TS-1 using amorphous SiO2 and its catalytic properties for hydroxylation of phenol in fixed-bed reactor by Hong Liu; Guanzhong Lu; Yanglong Guo; Yun Guo (pp. 153-161).
Titanium silicalite-1 (TS-1) has been synthesized using amorphous SiO2 as silicon source and tetrapropylammonium bromide (TPABr) as template. The effects of preparation parameters, such as silicon sources, crystallization temperature and time, aging time, H2O/SiO2, SiO2/TiO2, TPABr/SiO2 and n-butylamine (NBA)/SiO2, and nonionic surfactants on the physicochemical and catalytic properties of TS-1 were investigated in detail. The TS-1 samples were characterized by XRD, FT-IR, UV–vis, SEM, ICP-AES and N2 adsorption. In the fixed-bed reactor, the catalytic property of TS-1 for the phenol hydroxylation was tested. The studies show that the catalytic performance of TS-1 synthesized using amorphous SiO2 is close to that of the samples prepared with tetraethyl orthosilicalite (TEOS) for the phenol hydroxylation with H2O2. The crystallinity of the sample increases with an increase of the crystallization temperature, crystallization time, the ratio of SiO2/TiO2, SiO2/H2O and NBA/SiO2. TS-1 with smaller crystals can be obtained by increasing aging time, H2O/SiO2 and NBA/SiO2, and using the nonionic surfactants. Moreover, adding the nonionic surfactants in the matrix gel can increase the amount of Ti incorporated in framework of zeolite and reduces the amount of TiO2 in an extra framework.
Keywords: Titanium silicalite-1; Amorphous SiO; 2; Hydroxylation of phenol; Fixed-bed reactor
Hydrogenation of p-nitrophenol to metol using Raney nickel catalyst: Reaction kinetics by Sunil P. Bawane; Sudhirprakash B. Sawant (pp. 162-170).
Kinetics of the liquid-phase catalytic hydrogenation of p-nitrophenol (PNP) to p-aminophenol (PAP) and its conversion to metol have been investigated over a wide range of operating conditions. The effects of speed of agitation, hydrogen partial pressure, catalyst loading, substrate concentration and temperature on both the reactions have been reported. The effects of various solvents (2-propanol, methanol, dimethylformamide) on both the reactions have been investigated. Both the reactions were found to be first order with respect to the hydrogen partial pressure, first order with respect to PNP concentration for PAP formation and zero order with respect to substrate for metol formation. The experimental data could be fitted to the model involving a surface reaction controlling mechanism with dissociative adsorption of hydrogen for PNP hydrogenation and molecular adsorption of hydrogen for metol formation. The activation energies for the catalytic hydrogenation of PNP and metol formation were found to be 47 and 51kJmol−1, respectively.
Keywords: Hydrogenation; P; -nitrophenol; P; -aminophenol; Metol; Raney nickel
Physical properties of the crosslinked cellulose catalyzed with nanotitanium dioxide under UV irradiation and electronic field by Chyung-Chyung Wang; Cheng-Chi Chen (pp. 171-179).
Four different carboxylic acids (1,2,3,4-butane tetracarboxylic acid (BTCA), maleic acid (MA), succinic acid (SUA), and citric acid (CA)) were used as crosslinking agents for finished cotton fabrics in the presence of nanometer titanium dioxide catalyst under the irradiation of ultraviolet (UV) light and/or an electronic field (EF). We find that the dry crease recovery angle, wet crease recovery angle, and softness improvement percentages of the treated fabrics for all the crosslinking agents are gradually increased with the increasing of irradiation time period, but the TSR values decreased in all cases. The crease recovery and softness properties for the various crosslinking agents are ranked as BTCA>MA>CA>SUA at a given UV irradiation time period. The addition of EF treatment on the UV-irradiated fabrics improves the catalytic effects significantly. The spectra of Fourier transform infrared spectrophotometry reveal the crosslinking reaction between the carboxylic acid group of citric acid and the hydroxyl group of methylcellulose; this reaction could form ester and ether groups in the presence of nanometer TiO2 catalyst under UV irradiation and UV irradiation and EF treatment. The pictures of scanning electron microscopy and the electron spectroscopy for chemical analysis survey spectra show the surface deposition of acid crosslinking agents on the finished fibers and the crosslinking reaction between citric acid and cellulose molecule catalyzed with nanometer titanium dioxide under the irradiation of UV only and under the irradiation of UV and the treatment of EF separately.
Keywords: Crosslinking; Catalysts; FT-IR; ESCA; Crease recovery angle; UV irradiation; Photo-reduction; EF treatment
Polymer-supported metallocene catalysts for gas-phase ethylene/1-hexene polymerization by Long Wu; Jia-Min Zhou; David T. Lynch; Sieghard E. Wanke (pp. 180-191).
The ethylene and ethylene/1-hexene polymerization activities of seven catalysts, consisting of ( n-BuCp)2ZrCl2/MAO supported on five different types of spherical polymer beads, were determined for gas-phase polymerization at 1.4MPa ethylene pressure and initial 1-hexene concentrations of up to 40mol/m3. The catalytic activity for all the catalysts was highest at 80–90°C. Copolymerization activities were higher than homopolymerization activities; the average rates for 1h runs ranged from 0.1 to 4.1 and from 2.4 to 13kgPE/(molZrsMPa C2H4) for homo- and copolymerization, respectively. Specific rates decreased with increasing Zr content for copolymerization (range of Zr concentration 0.21–0.39mass%). The rates of 1-hexene incorporation decreased with increasing Al:Zr ratios (range of Al:Zr ratios 100–370). Most of the catalysts produced spherical copolymer particles without the production of fines. Molar masses of copolymers were lower than those of homopolymers, but they did not change appreciably with changes in 1-hexene concentration.
Keywords: Metallocene catalysts (supported); Supports (polymeric); Gas-phase polymerization; Morphology (polymer); Comonomer incorporation
Corrigendum to “Catalyst for ultra-low sulfur and aromatic diesel� [Appl. Catal. A: Gen. 282 (2005) 227–235]
by Roberto Galiasso Tailleur; Juan Ravigli; Samuel Quenza; Norma Valencia (pp. 192-192).