Lower Deactivation Rate Research Articles

Photocatalytic activity of dispersed TiO 2 particles deposited on glass fibers

Anatase TiO 2 particles were uniformly and dispersedly deposited on the surface of glass fibers by a liquid phase deposition (LPD) method from a TiF 4 aqueous solution upon addition of H 3BO 3 at 60 °C and then calcined at 60, 300 and 500 °C. The photocatalytic activity of the samples was evaluated by the photocatalytic oxidation of nitrogen monoxide (NO) in the gaseous phase. It was found that calcination temperatures obviously influenced the surface morphology and photocatalytic activity of the TiO 2 particles deposited on the glass fibers. At 300 °C, the TiO 2 samples exhibited the highest photocatalytic activity for the photocatalytic oxidation of NO and for the further conversion of NO 2 (from NO 2 to HNO 3) due to the enhancement of crystallization of anatase TiO 2 particles. At 500 °C, the photocatalytic activity of the sample decreased significantly due to the dropping of many TiO 2 particles from the glass fibers. Compared with the TiO 2 film photocatalyst, the TiO 2 particles deposited on the glass fibers exhibited a lower deactivation rate.

Cu catalyst system with phosphorous containing bidendate ligand for living radical polymerization of MMA

The polymerization of methyl methacrylate (MMA) was carried out using CuBr/bidentate phosphorus ligand catalyst systems. MMA polymerization with CuBr/ phosphine-phosphinidene (PP) exhibited high conversion (≈80%) in 5 h at 90°C along with a linear increase of ln([M]0/[M]) versus time, indicating constant concentration of the propagating radicals during the polymerization. The molecular weight of the prepared PMMA tended to increase with conversion, suggesting the living polymerization characteristic of the system. On the other hand, a large difference between the measured and theoretical molecular weight and a broad molecular weight distribution were observed, implicating possible incomplete control over the polymerization. This may have been caused by the low deactivation rate constant (k deact ) of the system. The lowk deact would result in irreversible generation of radicals instead of reversible activation/deactivation process of ATRP. Polymerizations performed at different ligand to CuBr ratios and different monomer to initiator ratios did not afford better control over the polymerization, suggesting that the controllability of CuBr/phosphorus ligand system for ATRP is inherently limited.

Role of acidity and microporous structure in alternative catalysts for the transformation of methanol into olefins

The transformation of methanol into light olefins (C 2–C 4) has been studied on several acid catalysts prepared by agglomerating different microporous acid phases (SAPO-11, SAPO-18, SAPO-34 and beta-zeolites) with bentonite and inert alumina. SAPO-11s and beta-zeolites have been prepared under different conditions and, consequently, they have different porous structure, total acidity and site acid strength. An analysis is made of the influence of their properties (micropore diameter, total acidity, acid strength and site density on their surface) on the kinetic behaviour of the catalysts (initial conversion and selectivity to olefins and deactivation rate). The catalyst SAPO-18 has a lower deactivation rate than the SAPO-34 due to a slightly lower acid strength and to a lower density of strong acid sites on the surface. This behaviour and the lower preparation cost make SAPO-18 an interesting alternative to SAPO-34, which is the one used in industry in the MTO process.

Ni-exchanged AlMCM-41—An efficient bifunctional catalyst for ethylene oligomerization

A series of Ni-exchanged AlMCM-41 catalysts with carefully controlled concentrations of metallic and acidic sites was prepared, characterized, and tested in ethylene oligomerization performed in slurry batch mode. The mesoporous materials were characterized using various techniques including X-ray diffraction, nitrogen sorption measurements, temperature-programmed desorption of NH 3, thermal gravimetric analysis, and temperature-programmed reduction. The presence of a uniform pore-size distribution in the ordered mesoporous materials is very favorable for the oligomerization process. High activities were obtained for most of tested catalysts, and the reaction was highly selective, resulting almost exclusively in olefins with an even number of C 4–C 12 carbon atoms. Both metal and acid sites are required for the activation of ethylene oligomerization. However, the samples with lower acidity showed very high reaction activity and stability due to their lower deactivation rate. The catalytic activity and product spectrum showed a pronounced dependence on the oligomerization conditions. Thus, the ethylene conversion goes through a maximum at 150 °C reaction temperature, and increased linearly when the pressure increased from 2 to 5 MPa. n-Heptane was found to be an efficient solvent for the ethylene oligomerization.

Development of sulfur tolerant catalysts for the synthesis of high quality transportation fuels

In this paper, results concerning the development of sulfur tolerant catalysts for Fischer–Tropsch synthesis (FTS), C 2+ alcohol synthesis, methanol and/or DME synthesis are presented. In the FTS reaction on Fe using H 2-rich syngas such as the biomass-derived syngas, the composition of catalyst pretreatment gas and the addition of MnO on Fe had strong impacts on its sulfur resistance as well as activity. Especially the Fe/MnO catalyst pretreated with CO showed a much lower deactivation rate and a higher FTS activity than an Fe/Cu/K catalyst in the presence of H 2S. For C 2+ alcohol synthesis a novel preparation method was developed for a highly active MoS 2-based catalyst that is well known as the sulfur tolerant catalyst. Besides some metal sulfides were found to show higher CO hydrogenation activities than MoS 2. In particular, both Rh and Pd sulfides were active and selective for the methanol synthesis. Modified Pd sulfide catalyst, i.e. sulfided Ca/Pd/SiO 2, showed an activity that was about 60% of that of a Cu/ZnO/Al 2O 3 catalyst in the absence of H 2S. This catalyst preserved 35% of the initial activity even in the presence of H 2S. The sulfided Ca/Pd/SiO 2 mixed with γ-Al 2O 3 was also available for in situ DME synthesis in the presence of H 2S.

Synthesis of 1,1‐diethoxyethane using a continuous flow reactor: catalyst deactivation and effect of feed purity and of solvent addition

AbstractThe synthesis of 1,1‐diethoxyethane from ethanol and acetaldehyde was studied in a continuous flow reactor using Amberlyst 15 as catalyst. The resin underwent an important activity loss with both analytical quality reagents and industrial raw materials. The deactivation was related to a deterioration in acidity as a consequence of sulfonic group hydration mainly promoted by water from reaction. A higher ethanol conversion and a lower deactivation rate at long time on‐stream were observed when n‐hexane was added to the feed. Copyright © 2004 Society of Chemical Industry

A series of NiMo/Al 2O 3 catalysts containing boron and phosphorus : Part II. Hydrodenitrogenation and hydrodesulfurization using heavy gas oil derived from Athabasca bitumen

The hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) activity of a series of NiMo/Al 2O 3 catalyst containing boron (B) and phosphorus (P) were tested in a trickle bed reactor using heavy gas oil derived from Athabasca bitumen. Detailed characterization of these catalysts is given in Part I of this paper. Addition of B and P caused the formation of extremely strong acid sites on the catalyst and enhanced its HDN activity. The total (TN), basic (BN) and non-basic nitrogen (NBN) conversions increased from 61.9 to 78.0 wt.%, from 78.9 to 93.0 wt.% and from 52.8 to 70.0 wt.%, respectively, with the increase in B concentration from 0 to 1.7 wt.% to NiMo/Al 2O 3 catalyst. Similarly, TN, BN and NBN conversions increased from 61.9 to 78.4 wt.%, from 78.9 to 91.0 wt.%, and from 52.8 to 71.6 wt.% with the addition of 2.7 wt.% P. Though the addition of B and P to NiMo/Al 2O 3 catalyst did not show any significant effect on S conversion, the HDN and HDS activities of the catalyst containing 1.7 wt.% B and the one containing 2.7 wt.% P are comparable to those of a commercial catalyst. The activity over extended period indicated that catalysts L and K were more stable (lower deactivation rate) in terms of nitrogen removal activity than catalyst B (reference catalyst). On the other hand, the stability for sulfur removal was comparable with catalyst B. Selected catalysts after use were characterized using BET surface area, TPR, TPD and SEM techniques which were correlated further with their activities.

Benzene Selective Oxidation with N 2 O on Fe/MFI Catalysts: Role of Zeolite and Iron Sites on the Deactivation Mechanism

The catalytic performances of Fe-zeolites having MFI structures and in which the Fe introduced either by ion exchange or during the hydrothermal synthesis has undergone partial framework to extra-framework migration induced by controlled heat treatment are reported. In particular, the catalytic behavior as function of time-on-stream and the formation of carbonaceous species were studied. The results suggest that only a small fraction of the iron is active in the selective oxidation of benzene to phenol in the presence of N2O. It is suggested that the active fraction is formed by isolated iron ions in a pseudo-octahedral configuration with the sites positioned in hydroxyl nests (defects) of the zeolite and is selective in phenol formation as a result of in situ reduction during the catalytic tests. Two possible pathways of carbonaceous species were identified, the first through the intermediate further hydroxylation of phenol and the second through the coupling of phenol with benzene or another phenol molecule. This second pathway is the dominant mechanism of formation of carbonaceous species, although the relative rate of the two pathways depends on the zeolite characteristics and iron loading. It is also suggested that the second pathway depends on the strong chemisorption of phenol, probably on Lewis acid sites, which hinders the fast back-desorption of phenol out from the zeolite channels and thus favors the formation of carbonaceous species. Catalysts prepared by hydrothermal treatment show a lower rate of deactivation than those prepared by ion exchange, although the latter show a comparable productivity to phenol for amounts of iron in extra-framework positions around 20 to 30 times lower. The results also indicate that the presence of Al in the zeolite framework is beneficial for reducing the rate of deactivation as compared to that of Fe-silicalite samples.

The Effects of Silanation of External Acid Sites on the Structure and Catalytic Behavior of Mo/H–ZSM5

The selective silanation of external acid sites in H–ZSM5 using large organosilane reagents was used to decrease the density of such sites and the number of MoOx species retained at external surfaces during cation exchange using MoO3/H–ZSM5 physical mixtures. On samples prepared using silica-modified H–ZSM5, acid sites, MoOx precursors, and the active MoCx species formed during CH4 reactions at 950 K reside predominately within zeolite channels, where spatial constraints inhibit bimolecular chain-growth pathways. As a result, these samples show higher selectivities to desired C2–C6 aromatics and lower deactivation rates than those prepared from untreated H–ZSM5. CH4 conversion rates are also higher on Mo/H–ZSM5 samples prepared from silanated H–ZSM5, because of the more complete exchange and higher dispersion of MoOx precursors. In situ X-ray absorption measurements showed that silanation of external OH groups does not influence the structure of the MoOx precursors formed during synthesis or of active MoCx species formed during CH4 reactions from exchanged (Mo2O5)2+ dimers. The substantial absence of acidic OH groups and of MoCx species sites at unconstrained external surfaces leads to significant improvements in activity, selectivity, and stability for Mo/H–ZSM5 catalysts for CH4 pyrolysis reactions.

Characterization and dehydrogenation activity of Cr-added electroless plated copper catalyst

Copper catalysts with chromium addition, prepared by the electroless plating method, were investigated. Dehydrogenation of n-butanol was conducted to study the effect of chromium addition on the catalysts. Copper loading on γ-Al 2O 3 was fixed at 15% and Cr addition varied from 1 to 5%. Experimental results show that the copper catalyst activity depends not only on the chromium loading but also on the addition procedure. The catalysts with chromium addition present higher catalyst activity and lower deactivation rate than the pure one. X-ray diffraction (XRD) patterns show that the addition would increase copper dispersion and hence decrease copper crystallite size formed on the support. Temperature-programmed reduction (TPR) profiles indicate that the addition of chromium affects the copper reduction temperature. Chromium addition would cause the TPR curve to shift slightly to lower temperature.

Influence of coke deactivation and vanadium and nickel contamination on the performance of low ZSM-5 levels in FCC catalysts

The effect of coke deposition on the product selectivity of FCC catalyst/ZSM-5 mixtures has been studied in the presence and absence of contaminant metals. In order to investigate the influence of coke deactivation on activity and selectivities experiments were also performed with coke-free and pre-coked FCC catalysts and FCC catalyst/ZSM-5 blends. The cracking reactions were conducted with a heavy vacuum gas–oil in a microactivity test unit at high temperature and short contact time. The effectiveness of ZSM-5 is mainly reflected by the selectivities to C 3 and C 4 products, especially olefins, and these selectivities revealed that the deactivation of ZSM-5 and FCC catalyst by coke was similar in the absence of metals. In the presence of metals ZSM-5 was less deactivated by coke formation than the FCC catalyst resulting in an enhanced effectiveness of ZSM-5 in both, the non-coked ZSM-5/FCC catalyst combinations and the pre-coked ZSM-5/FCC catalyst blends. The selectivities of C 6–C 9 olefins were not affected by pre-coking of the FCC catalyst prior to microactivity testing either in the metals-free or in the metallated state. C 6–C 9 olefins are reactants for ZSM-5 and therefore, the effects of coke deactivation on ZSM-5 performance cannot be ascribed to different olefin concentrations in the gasoline range. Coking of catalysts lowered the cracking activity of the FCC catalysts and therefore the reaction severity was boosted to achieve a given conversion and this was done by increasing the catalyst mass. Hence, the increasing effectiveness of metallated ZSM-5 with increasing coke-on-catalyst can be ascribed to both, the increase in FCC catalyst/ZSM-5 mass in the reactor at constant conversion and the lower deactivation rate of ZSM-5 by coke compared with the decay of the FCC catalyst.

Deactivation of Cu/ZnO/Al2O3 Methanol Synthesis Catalyst by Sintering

The loss of Cu/ZnO/Al2O3 activity for methanol synthesis has been studied over 50 h under a range of synthesis gas compositions. Experiments have been carried out at differential and finite conversions in order to compare deactivation under the pure feed to that in the presence of products. Under differential conversion, it was found that the degree of deactivation was related to the CO concentration, being particularly acute under CO/H2. Under CO/H2, there was a close correlation between activity loss and loss of Cu surface area, suggesting that an important cause of deactivation is sintering, which may be promoted by over-reduction of Cu. At finite conversion with CO/H2 feed the deactivation was less severe. This lower rate of deactivation is most likely due to exposure of the catalyst to products that can stabilize oxidized Cu species. Interestingly, under CO2/H2, the deactivation was negligible at differential conversion. However some deactivation was apparent at finite conversion. The exposure of the catalyst to the products, CO and water, at finite conversion can explain these results.

The Effect of Potassium and Tin on the Hydrogenation of Ethylene and Dehydrogenation of Cyclohexane over Pt(111)

Stable ordered structures of Sn on Pt(111) (maximum coverage of 0.33 monolayers) were used as model catalysts to test the effect of tin and potassium on the hydrogenation of ethylene at 300 K and dehydrogenation of cyclohexane at 573 K and at pressures of 15 Torr of hydrocarbon and 100 Torr of H2. Co-adsorption of tin and potassium on Pt(111) resulted in the direct interaction between potassium, tin, and platinum as verified by temperature-programmed desorption of CO. Tin deposition yielded a maximum in the turnover rate as a function of Sn coverage for ethylene hydrogenation and cyclohexane dehydrogenation with maxima at about 0.2 monolayers of tin and a turnover rate 75% higher than on clean Pt(111). This enhancement was explained by a lower rate of deactivation as tin was added. In contrast, the addition of potassium to Pt and Pt/Sn produced only a monotonic decrease in cyclohexane dehydrogenation. In an industrial system, where a higher tin coverage is used, interaction of tin with potassium may form an effective site blocker which could lower deactivation rates.

MxOy/SO42−/Dealuminated Zeolite β (M=Ti, Fe) as Novel Catalysts for Alkylation of Isobutane with 1-Butene

Abstract A new kind of MxOy/SO42−/H-form dealuminated β (DHβ) catalysts prepared here were applied to alkylation of isobutane with 1-butene. The group of MxOy/SO42−/DHβ (M=Ti, Fe) catalysts has a lower rate of deactivation and higher selectivity of this alkylation than other group of Hβ and DHβ. It is proposed that the strong acid sites corresponding to the active sites for this alkylation can be formed by the interaction among DHβ, MxOy, and SO42−.

Reforming of methane with carbon dioxide over Ni/Al 2O 3 catalysts: Effect of nickel precursor

The catalytic activities of Ni/γ-Al 2O 3 catalysts prepared using different nickel precursor compounds were studied for the reaction of methane reforming with CO 2. It is found that the nickel precursor employed in the catalyst preparation plays an important role. The catalyst based on nickel nitrate exhibited higher catalytic activity and stability over a 24-h test period than the other two catalysts derived from nickel chloride and nickel acetylacetonate. A comprehensive characterisation of the catalysts showed that the weak interaction between Ni particles and γ-Al 2O 3 resulted in more active sites on Ni nitrate-derived Ni/γ-Al 2O 3 catalyst. Coking studies showed that carbon deposition on Ni catalysts derived from inorganic precursors (nitrate and chloride) were more severe than on the organic precursor-derived catalyst. However, the Ni nitrate-derived catalyst was found to have the highest stability (or lowest deactivation rate) mainly due to the active carbon species (–C–C–) of the resulting graphitic structure and their close contact with the metal particles. In contrast, the carbon formed on Ni–AA catalyst (from Ni acetylacetonate) is dominated by inactive –CO–C– species, thus leading to a rapid accumulation of carbon in this catalyst and more severe deactivation.

Physicochemical Characterisation and Catalytic Activity of Primary Amine Templated Aluminosilicate Mesoporous Catalysts

Primary amines are used as structure-directing agents in the room temperature assembly of aluminosilicate inorganic species to yield mesoporous materials with physical and textural properties similar to those of MCM-41 but with substantially higher Brønsted acidity. Si and Al are incorporated into the mesoporous framework in proportions dependent on the gel Si/Al ratio. Calcination of the as-synthesised material to remove the occluded amine generates Brønsted acid sites which (depending on Si/Al ratio) are stronger or comparable in strength to those on zeolite-HY (Si/Al=3.65) but weaker than those on ultrastable-Y zeolite (USY). The materials, designated Al-MMS, exhibit higher Brønsted acidity and catalytic activity for the cracking of cumene compared to equivalent aluminosilicate MCM-41 materials or to amorphous silica-alumina and show considerable stability to catalytic deactivation. Al-MMS samples with Si/Al ratio ≤20 have catalytic activity higher than the zeolite-HY but exhibit a lower rate of deactivation compared to the zeolite. Ageing of the materials (for 1 year in the calcined form) has no significant effect on their acidity and catalytic activity. Hexagonal ordering and total Brønsted acidity (but not acid strength) of the Al-MMS materials may be improved by using prepolymerised aluminosilicate inorganic precursors.

The oligomerization of 1-butene using NaY zeolite ion-exchanged with different nickel precursor salts

A number of catalysts were prepared by ion exchanging NaY extrudates with different nickel precursor salts. These nickel exchanged NaY catalysts (NiNaY) were used to oligomerize butenes in the liquid phase using a batch reactor. The acidity of catalysts, determined by temperature programmed desorption, was found to be dependent on the type of nickel precursor salt. The catalyst derived from nickel acetate was found to have the highest acid strength, whereas the one derived from nickel chloride had the weakest acid strength. The nickel chloride catalyst apparently had the highest activity of all those tested; this is attributed to the low deactivation rate of this catalyst. The addition of ammonium fluoride and ammonium chloride to NiNaY derived from a nickel nitrate precursor salt resulted in an enhancement of oligomerization activity. Temperature programmed desorption (TPD) studies indicate that the addition of halide anions lead to a modification of acid sites in the original NiNaY. The catalyst formed from the ammonium fluoride promotion showed the highest activity, best dimer selectivity and lowest deactivation rate of all the halide promoted catalysts tested under the reaction conditions used in this study. A study of the effect of temperature on the oligomerization reaction revealed that the reaction is diffusion-rate limited under the conditions used in this study. Solvent was found to play an important role on activity and deactivation of the NiNaY catalysts.

The oligomerization of butenes with partially alkali exchanged NiNaY zeolite catalysts

A number of catalysts were prepared by exchanging NaY zeolite with various amounts of nickel (NiNaY) as well as partially exchanging NaY zeolite with alkali and alkaline-earth cations (M) followed by nickel promotion (NiMNaY). These catalysts were used to oligomerize butenes in the liquid phase. For the NiMNaY catalysts prepared from similar concentrations of nickel chloride, the nickel loading decreased with increase in the cationic size of M. The acidity of catalysts was measured using temperature programmed desorption of ammonia. The NiNaY catalysts showed an increase in acid concentration with nickel loading. For the NiMNaY catalysts, a linear correlation between the acid concentration and the Sanderson electronegativity of M was found. The oligomerization activity of NiNaY and NiMNaY catalysts increased with nickel loading and acidity. It was observed that the increase in activity also led to an increase in the deactivation rate. This is attributed to the increased adsorption of olefins on the more acidic catalysts leading to the formation of long chain oligomers that foul the catalysts. For the catalysts with similar activities, the dimer selectivity was found to increase with cationic size of M, but decreased with increase in Sanderson's electronegativity of M. This improvement in catalyst stability imparted by M is probably due to the partial blocking of windows for the hexagonal prisms and/or sodalite cages of the nickel exchanged catalysts. The NiCsNaY catalyst was found to be an almost exclusive dimer selective catalyst and has the lowest deactivation rate.

Condensation of allyl alcohol with ammonia over phosphoric acid catalyst supported on controlled pore glass

The condensation of allyl alcohol with ammonia was studied over phosphoric acid catalyst supported on controlled pore glass (CPG). The above catalyst was compared with silica supported phosphoric acid. The CPG supported catalyst showed higher selectivity and lower rate of deactivation than the corresponding silica supported one. The above difference can be attributed to both the boron content and the large pore size of the CPG support.

Reactivation of Coked H-ZSM-5 by Treatment with Hydrogen and Alkanes

The conversion of methanol to hydrocarbons on zeolite H-ZSM-5, in particular the long-term stability of the catalyst, was studied under different reaction conditions. Whereas no significant change in the product distribution was observed, hydrogen and alkane-containing recycle gases show lower deactivation rates than nitrogen. In addition, spent catalysts were partially reactivated by alkane treatment, increasing the time on stream before an oxidative regeneration procedure is required. Lower alkanes such as propane and isobutane yield the best results. The influence of hydrogen-containing gases on the deactivation rate and on the nature of coke on zeolite H-ZSM-5 indicates dissociative adsorption of hydrogen and alkanes on a few sites with enhanced activity. Surface hydrogen species formed by adsorption of alkanes are assumed to make possible the hydrocracking of carbonaceous deposits.