Transesterification of triacetin with methanol on Nafion® acid resins

Although homogeneous alkali catalysts (e.g., NaOH) are commonly used to produce biodiesel by transesterification of triglycerides (vegetable oils and animal fats) and methanol, solid acid catalysts, such as acidic resins, are attractive alternatives because they are easy to separate and recover from the product mixture and also show significant activity in the presence of fatty acid impurities, which are common in low-cost feedstocks. To better understand solid acid catalyst performance, a fundamental transesterification kinetic study was carried out using triacetin and methanol on Nafion^® (perfluorinated-based ion-exchange resin) catalysts. In particular, Nafion^® SAC-13 (silica-supported Nafion) and Nafion^® NR50 (unsupported Nafion) were investigated, because both show great promise for biodiesel-forming reactions. The reaction kinetics for a common homogeneous acid catalyst (H₂SO₄) were also determined for comparison. Liquid-phase reaction was performed at 60 °C using a stirred batch reactor. The swelling properties of the resin in solvents of diverse polarity that reflect solutions typically present in a biodiesel synthesis mixture were examined. The initial reaction rate was greatly affected by the extent of swelling of the resin, where, as expected, a greater effect was observed for Nafion^® NR50 than for the highly dispersed Nafion^® SAC-13. The reaction orders for triacetin and methanol on Nafion^® SAC-13 were 0.90 and 0.88, respectively, similar to the reaction orders determined for H₂SO₄ (1.02 and 1.00, respectively). The apparent activation energy for the conversion of triacetin to diacetin was 48.5 kJ/mol for Nafion^® SAC-13, comparable to that for H₂SO₄ (46.1 kJ/mol). Selective poisoning of the Brønsted acid sites on Nafion^® SAC-13 using pyridine before transesterification revealed that only one site was involved in the rate-limiting step. These results suggest that reaction catalyzed by the ion-exchange resin can be considered to follow a mechanism similar to that of the homogeneous catalyzed one, where protonated triglyceride (on the catalyst surface) reaction with methanol is the rate-limiting step.     

Methane Partial Oxidation Using A (La0.6Sr0.4)(Ga0.8Mg0.05Co0.15)O3–δ Membrane

A novel sulfonated carbon composite solid acid was successfully prepared by the pyrolysis of a polymer matrix impregnated with glucose followed by sulfonation. The title catalyst has higher acid site density, better esterification activity of both small and large free fatty acids (acetic acid and palmitic acid), and better reusability than the previously reported carbon-based catalyst prepared by sulfonating pyrolyzed sugar. This catalyst also exhibited higher esterification activity than tungstated zirconia (WZ) and Silica-Supported Nafion (Nafion^®SAC-13). The higher activity of the sulfonated carbon composite solid acid catalyst was clearly due to the presence of a much higher acid site density than any of the other catalysts.     

A comparative study of gas phase esterification on solid acid catalysts

For the first time, a comprehensive comparison of the intrinsic activities of solid acid catalysts in terms of turnover frequency (TOF) is reported for the gas-phase esterification of acetic acid with methanol. The catalysts studied included a zeolite (Hβ), two modified zirconias (sulfated zirconia, SZ; and tungstated zirconia, WZ), and an acidic resin-silica composite (Nafion/silica, SAC-13). Activities on a per weight basis decreased in the following order: Hβ ～ SAC-13 ? SZ >  WZ at 130 °C. However, on a rate-per-site basis (TOF), all catalysts showed comparable activities. The TOF results suggest that the acid sites of these catalysts have similar capacity for effectively catalyzing esterification. All catalysts deactivated to a quasi-steady-state rate with TOS. Regeneration experiments suggested that catalyst deactivation was due mainly to site blockage by carbonaceous deposits. Selective poisoning experiments showed that the reaction predominately took place on Brønsted acid sites.     

Novel catalysts for selective dehalogenation of CCl2F2(CFC 12)

Several supported and unsupported metal carbide catalysts were synthesized, characterized, and studied for their activity in the dehalogenation of CCl₂F₂ (CFC 12). Their catalytic properties were compared to those of a standard palladium catalyst. The turnover rates of the supported carbides were found to be higher than the unsupported carbides, but both deactivated quickly in the initial stages of reaction. X-ray photoelectron spectroscopic analysis of fresh and spent catalysts showed deposition of excessive amounts of carbon during the reaction which could be the cause of deactivation.     

Study on deactivation of Cu–Zn–Al catalysts in the synthesis of N-ethylethylenediamine

The performance of a Cu–Zn–Al catalyst employed in the synthesis of N-ethylethylenediamine from ethylenediamine and ethanol was studied. The results showed that the activity of the Cu–Zn–Al catalyst decreased with time-on-stream. Fresh and deactivated catalysts were characterized by XRD, XPS, N₂ adsorption–desorption and TEM. It was found that the crystallite size of Cu and ZnO in the deactivated catalyst were much bigger than those for the fresh catalyst. In addition, channels in the deactivated catalyst were blocked by carbonaceous deposits, so the surface area and pore volumes of the deactivated catalyst were much smaller than in the fresh catalyst. Therefore, it was concluded that the deactivation of the Cu–Zn–Al catalyst was mainly caused by the growth in the Cu and ZnO crystallite sizes and carbonaceous deposits.     

Regeneration of Lamina TS-1 Catalyst in the Epoxidation of Propylene with Hydrogen Peroxide

The deactivation and regeneration of the lamina titanium silicalite (TS-1) catalyst for the epoxidation of propylene with dilute H₂O₂was investigated in a fixed-bed reactor. In the scale-up experiment, the dosage of the lamina TS-1 catalyst is 2. 5 kg, after 1000 h reaction the catalyst still exhibits good performance and further increases the reaction time, the conversion of H₂O₂begins to decrease. TG and BET analyses of the deactivated catalysts show that the main species occluded within the zeolite pore are propylene oxide oligomers, and these species occupying the active Ti site and blocking the pores of the lamina TS-1 are the main reason for the deactivation of catalyst. The deactivated catalyst can be regenerated by different regeneration methods. The activity of deactivated catalysts regenerated by dilute H₂O₂or heat treatment by using air or nitrogen as a calcination media can be fully recovered, but a decline in propylene oxide (PO) selectivity of the regenerated catalyst has been observed during the first hours of reaction. However, water vapor treatment of the deactivated catalyst can improve the PO selectivity with the same activity as that of the fresh lamina TS-1 catalyst.     

Catalysis and deactivation of montmorillonite K10 in the aryl <Emphasis Type="Italic">O</Emphasis>-glycosylation of glycosyl trichloroacetoimidates

The catalysis of montmorillonite K10 (MK10) for aryl O-glycosylation of glycosyl trichloroacetimidates was investigated. It was found that the catalyst MK10 is deactivated gradually in the recycle glycosylation. The fresh and the deactivated catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Thermogravimetric analysis (TGA), and N₂ adsorption-desorption. The results show that the eliminated trichloroacetamide molecule deposits on the MK10, which blocks and poisons the active sites, resulting in the deactivation of the catalyst. The regeneration of the deactivated MK10 by calcination was studied preliminarily.     

Rh<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Pd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Nanoparticle Composition Dependence in CO Oxidation by NO

Abstract  

Bimetallic 15 nm Pd-core Rh-shell Rh_1−x Pd _x nanoparticle catalysts have been synthesized and studied in CO oxidation by NO. The catalysts exhibited composition-dependent activity enhancement (synergy) in CO oxidation in high NO pressures. The observed synergetic effect is attributed to the favorable adsorption of CO on Pd in NO-rich conditions. The Pd-rich bimetallic catalysts deactivated after many hours of oxidation of CO by NO. After catalyst deactivation, product formation was proportional to the Rh molar fraction within the bimetallic nanoparticles. The deactivated catalysts were regenerated by heating the sample in UHV. This regeneration suggests that the deactivation was caused by the adsorption of nitrogen atoms on Pd sites.     

NiCoFe/C cathode electrocatalysts for direct ethanol fuel cells

A direct ethanol fuel cell (DEFC), which is less prone to ethanol crossover, is reported. The cell consists of PtRu/C catalyst as the anode, Nafion^® 117 membrane, and Ni–Co–Fe (NCF) composite catalyst as the cathode. The NCF catalyst was synthesized by mixing Ni, Co, and Fe complexes into a polymer matrix (melamine-formaldehyde resins), followed by heating the mixture at 800 °C under inert atmosphere. TEM and EDX experiments suggest that the NCF catalyst has alloy structures of Ni, Co and Fe. The catalytic activity of the NCF catalyst for the oxygen reduction reaction (ORR) was compared with that of commercially available Pt/C (CAP) catalyst at different ethanol concentrations. The decrease in open circuit voltage (V_oc) of the DEFC equipped with the NCF catalysts was less than that of CAP catalyst at higher ethanol concentrations. The NCF catalyst was less prone to ethanol oxidation at cathode even when ethanol crossover occurred through the Nafion^®117 film, which prevents voltage drop at the cathode. However, the CAP catalyst did oxidize ethanol at the cathode and caused a decrease in voltage at higher ethanol concentrations.     

Deactivation in Continuous Deoxygenation of C18-Fatty Feedstock over Pd/Sibunit

Catalytic continuous deoxygenation of stearic acid, ethyl stearate and tristearin without any solvents was investigated using Pd/Sibunit as a catalyst in a trickle bed reactor at 300 °C. The main emphasis was to investigate the effect of gas atmosphere and catalyst deactivation. In addition to liquid-phase analysis made offline by GC, also online gas-phase analysis with IR were performed. The main liquid-phase product coming from all reactants was n-heptadecane. In addition to deoxygenation, which was observed for all substrates, also C₁₈ and C₁₆ alkanes were formed from tristearin. The relative ratios between stearic acid, ethyl stearate and tristearin conversions to alkanes after 3 days time-on-stream were 2.8/2.3/1.0, respectively using 5 % H₂/Ar as a gas atmosphere, whereas rapid catalyst deactivation occurred with all substrates under H₂-lacking atmosphere. The spent catalyst’s specific surface area profile along the downward reactor was maximum in the middle of the catalyst beds with the highest pore shrinking in the beginning and at the end of the reactor catalyst segments in the case of stearic acid and tristearin deoxygenation whereas that decreased consecutively as ethyl stearate passed through the reactor.     

Partial oxidation of benzene catalyzed by vanadium chloride in novel reaction-extraction-regeneration system

This paper investigates the liquid-phase partial oxidation of benzene to phenol in a novel system consisting of reactor, extractor and regenerator. Since vanadium catalyst (V³⁺) is oxidized in the reactor and therefore deactivated, the regenerator with Pd or Pt catalyst and H₂ feed is employed to regenerate the deactivated vanadium. The V⁴⁺ ion can be reduced to V³⁺ and consequently the phenol production can be enhanced. Although the regenerator can regenerate vanadium catalyst and the reaction can proceed for over 100 h, some V⁴⁺ is still present. The feed position of benzene and catalyst solution have the influence on mixing condition in the reactor and interface area between benzene and catalyst solution. Counter current flow operation with the feeds of catalyst solution and benzene at the top and the bottom respectively shows the highest phenol production. The operating temperature of reactor, extractor and regenerator showed insignificant effect on phenol production rate.     

Catalysis and deactivation of montmorillonite K10 in the aryl O-glycosylation of glycosyl trichloroacetoimidates

The catalysis of montmorillonite K10 (MK10) for aryl O-glycosylation of glycosyl trichloroacetimidates was investigated. It was found that the catalyst MK10 is deactivated gradually in the recycle glycosylation. The fresh and the deactivated catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Thermogravimetric analysis (TGA), and N₂ adsorption-desorption. The results show that the eliminated trichloroacetamide molecule deposits on the MK10, which blocks and poisons the active sites, resulting in the deactivation of the catalyst. The regeneration of the deactivated MK10 by calcination was studied preliminarily.     

The Deactivation Modes of Cu/ZnO/Al2O3 and HZSM-5 Physical Mixture in the One-Step DME Synthesis

The CO₂ production by shift reaction and the deactivation process are the drawbacks of the One-Step DME Synthesis. Therefore, this contribution discusses possible deactivation modes taking into account the catalytic performance and the characterization of spent catalysts using XRD, TG and FTIR techniques. For this purpose a physical mixture that contains a commercial methanol catalyst and ZSM-5 was employed. It can be suggested that one of the main modes of catalyst deactivation is the hydrocarbon formation by MTG reactions. Changes in the interaction between Cu⁰ and ZnO should also be considered. The results show that both of them are affected by H₂/CO ratio.     

The nature of the deactivation of hydrothermally stable Ni/SiO2–Al2O3 catalyst in long-time aqueous phase hydrogenation of crude 1,4-butanediol

The deactivation of Ni/SiO₂–Al₂O₃ catalyst in hydrogenation of crude 1,4-butanediol was investigated. During the operation time of 2140 h, the catalyst showed slow activity decay. Characterization results, for four spent catalysts used at different time, indicated that the main reason of the catalyst deactivation was the deposition of carbonaceous species that covered the active Ni and blocked mesopores of the catalyst. The TPO and SEM measurements revealed that the carbonaceous species included both oligomeric and polymeric species with high C/H ratio and showed sheet. Such carbonaceous species might be eliminated through either direct H₂ reduction or the combined oxidation–reduction methodologies.     

Selective Isopropylation of Biphenyl to 4,4′-DIPB over Mordenite (MOR) Type Zeolite Obtained from a Layered Sodium Silicate Magadiite

Molybdenum carbide catalysts for water–gas shift (WGS) reaction were investigated to develop an alternate commercial LTS (Cu-Zn/Al₂O₃) catalyst for an onboard gasoline fuel processor. The catalysts were prepared by a temperature-programmed method and were characterized by N₂ physisorption, CO chemisorption, XRD and XPS. It was found that the Mo₂C catalyst showed higher activity and stability than the commercial LTS catalyst, even though both catalysts were deactivated during the thermal cycling runs. The optimum carburization temperature for preparing Mo₂C was in the range of 640–650 °C. It was found that the deactivation of the Mo₂C catalyst was caused by the transition of Mo^δ+ (IV < δ⁺ < VI, MoO_xC_y), Mo^IV and Mo₂C on the surface of the Mo₂C catalyst to Mo^VI (MoO₃) with the reaction of H₂O in the reactant. It was identified that molybdenum carbide catalyst is an attractive candidate for the alternate Cu-Zn/Al₂O₃ catalyst for automotive applications.     

Influence of the promoter's nature (nickel or cobalt) on the active phases ‘Ni(Co)MoS’ modifications during deactivation in HDS of diesel fuel

The characterization of various spent Ni(Co)MoP/Al₂O₃ catalysts has been performed in order to elucidate the active phase modifications undergone on the catalysts at operating conditions. Six catalysts coming either from industrial or pilot reactors were studied. The deactivation level (for hydrogenation reaction) can be determined by XPS analysis quantifying the ‘Ni(Co)MoS’ mixed phase amount. The spent catalyst active phases characteristics, at different levels of deactivation, firstly evidenced that the coke particularly influences the CoMo active phase (X-ray photoelectron spectroscopy) lowering the ‘CoMoS’ mixed phase amount. On the spent NiMo catalysts, most of the nickel is segregated (XPS, Extended X-ray Absorption Fine Structure, Transmission Electronic Microscopy/Energy Dispersive Spectroscopy) even after low residence time in the unit (pilot plant origin). In both cases it leads to the progressive deactivation of the catalyst. The coke does not seem to influence the ‘NiMoS’ mixed phase amount excepted at its life-end.     

A Comparative Study of 4-Methylphenol Hydrodeoxygenation Over High Surface Area MoP and Ni2P

Unsupported, high surface area MoP and Ni₂P catalysts were synthesized by adding citric acid (CA) to solutions of ammonium heptamolybdate and diammonium hydrogen phosphate or nickel nitrate and diammonium hydrogen phosphate, respectively, followed by drying (397?K), calcination (773?K), and reduction in H₂ (923?K). The addition of CA increased the surface area, decreased the particle size, and increased the CO uptake of the MoP and Ni₂P catalysts. At 623?K and 4.4?MPa, the Ni₂P was 2.3 times more active than the MoP on a mass basis and 6 times more active on a site basis for the hydrodeoxygenation of 4-methylphenol. However, the Ni₂P catalysts deactivated due to non-selective carbon deposition on the catalyst surface. Oxidation was excluded as a potential cause of deactivation over the Ni₂P catalysts. The rate of deactivation was well described by an exponential decay law. Deactivation was eliminated by operation at higher H₂ pressures (5.3 and 6.1?MPa) but the hydrogenation selectivity of the Ni₂P increased at these conditions. No deactivation was observed over the MoP catalysts at the conditions of the present study.     

Catalyst deactivation and regeneration in low temperature ethanol steam reforming with Rh/CeO2–ZrO2 catalysts

Rh/CeO₂–ZrO₂ catalysts with various CeO₂/ZrO₂ ratios have been applied to H₂ production from ethanol steam reforming at low temperatures. The catalysts all deactivated with time on stream (TOS) at 350 °C. The addition of 0.5% K has a beneficial effect on catalyst stability, while 5% K has a negative effect on catalytic activity. The catalyst could be regenerated considerably even at ambient temperature and could recover its initial activity after regeneration above 200 °C with 1% O₂. The results are most consistent with catalyst deactivation due to carbonaceous deposition on the catalyst.     

Deactivation phenomena of supported platinum catalysts during the hydrogenation of cyclopropane

Cyclopropane hydrogenation reaction was performed in a differential reactor operating at atmospheric pressure, 50‡C and H₂/C₃H₆ ratio of 9, and the deactivation of the catalysts during the reaction was investigated by observing the effects of the supports and the size of platinum crystallites, Owinglo the accumulation of the carbonaceous materials the platinum catalysts dispersed on the acidic supports such as γ-Al₂O₃, SiO₂-Al₂O₃ and Y-zeolite deactivated significantly, while no detectable deactivation was observed for the catalysts on the non-acidic supports of SiO₂ and active carbon. In addition smaller platinum particles on acidic supports were morevulnerable to the catalyst deactivation.     

Deactivation Studies of Rh/Ce0.8Zr0.2O2 Catalysts in Low Temperature Ethanol Steam Reforming

Rapid deactivation of Rh/Ce_0.8Zr_0.2O₂ catalysts during low temperature ethanol steam reforming was studied. A significant build-up of reaction intermediates, instead of carbon deposit, was observed at low reaction temperatures. This appears to be the cause of rapid catalyst deactivation. Co-feed experiments indicated that possible intermediate products acetone and ethylene caused more severe catalyst deactivation than other oxygenates such as acetic acid and acetaldehyde.