Catalytic Lifetime Research Articles

Fabrication of a nano-sized ZSM-5 zeolite with intercrystalline mesopores for conversion of methanol to gasoline

Carbon deposition during methanol to hydrocarbons leads to the quick deactivation of ZSM-5 catalyst and it is one of the major problems for this technology. Decreasing the crystal size or introducing mesopores into ZSM-5 zeolites can improve its diffusion property and decrease the coke formation. In this paper, nano-sized ZSM-5 zeolite with intercrystalline mesopores combining the mesoporous and nano-sized structure was fabricated. For comparison, the mesoporous ZSM-5 and nano-sized ZSM-5 were also prepared. These catalyst samples were characterized by XRD, BET, NH3-TPD, TEM, Py-IR and TG techniques and used on the conversion of methanol to gasoline in a fixed-bed reactor at T=405°C, WHSV=4.74h−1 and P=1.0MPa. It was found that the external surface area of the nano-sized ZSM-5 zeolite with intercrystalline mesopores reached 104m2/g, larger than that of mesoporous ZSM-5 (66m2/g) and nano-sized ZSM-5 (76m2/g). Catalytic lifetime of the nano-sized ZSM-5 zeolite with intercrystalline mesopores was 93h, which was only longer than that of mesoporous ZSM-5 (86h), but shorter than that of nano-sized ZSM-5 (104h). Strong acidity promoted the coke formation and thus decreased the catalytic lifetime of the nano-sized ZSM-5 zeolite with intercrystalline mesopores though it presented large external surface that could improve the diffusion property. The special zeolite catalyst was further dealuminated to decrease the strong acidity. After this, its coke formation rate was slowed and catalytic lifetime was prolonged to 106h because of the large external surface area and decreased weak acidity. This special structural zeolite is a potential catalyst for methanol to gasoline reaction.

Role of 12-Ring Channels of Mordenite in DME Carbonylation Investigated by Solid-State NMR

In this work, we have studied the role of the 12-ring channel of mordenite in DME carbonylation. Upon modification with pyridine, the catalytic lifetime of mordenite in DME carbonylation was prolonged dramatically although its activity decreased slightly and the induction period increased. 1H MAS NMR and PFG-NMR results demonstrated that the acid quantity decreased after pyridine was adsorbed, and the self-diffusion coefficient of CH4 decreased with the increase in pyridine quantity in the 12-ring channel. 129Xe NMR results reveal that Xe atoms are preferentially adsorbed in an 8-ring side pocket at low pressure; xenon can enter the 8-ring side pocket at high temperature through the 12-ring channels only. From these results, the function of the 12-ring with respect to the reaction rate is explored and a transfer path of reactants/products is proposed.

Thermo-Catalytic Methane Decomposition for Hydrogen Production: Effect of Palladium Promoter on Ni-based Catalysts

Hydrogen production from the direct thermo-catalytic decomposition of methane is a promising alternative for clean fuel production. However, thermal decomposition of methane can hardly be of any practical and empirical interest in the industry unless highly efficient and effective catalysts, in terms of both catalytic activity and operational lifetime have been developed. In this study, the effect of palladium (Pd) as a promoter onto Ni supported on alumina catalyst has been investigated by using co-precipitation technique. The introduction of Pd promotes better catalytic activity, operational lifetime and thermal stability of the catalyst. As expected, highest methane conversion was achieved at reaction temperature of 800 °C while the bimetallic catalyst (1 wt.% Ni -1wt.% Pd/Al2O3) gave the highest methane conversion of 70% over 15 min of time-on-stream (TOS). Interestingly, the introduction of Pd as promoter onto Ni-based catalyst also has a positive effect on the operational lifetime and thermal stability of the catalyst as the methane conversion has improved significantly over 240 min of TOS.

Synthesis of SAPO-18 with low acidic strength and its application in conversion of dimethylether to olefins

SAPO-18 molecular sieve was synthesized by a dry gel conversion (DGC) and hydrothermal (HT) synthesis methods using methyltriethoxysilane as the only Si source (DGC-Me-SAPO-18 and HT-Me-SAPO-18). Their physicochemical and catalytic properties on dimethylether-to-olefin (DTO) reaction were compared with those of conventional SAPO-18 molecular sieves synthesized by a hydrothermal synthesis method (HT-SAPO-18). An NH3-TPD measurement revealed that the desorption peak position of Brønsted acid of the Me-SAPO-18 samples moved to lower temperature, indicating that Brønsted acidic strength of the Me-SAPO-18 samples was lower than that of the HT-SAPO-18 samples. The DME conversions and yields of light olefins over DGC-Me-SAPO-18 decreased at a slower rate than those of HT-SAPO-18. The decreased acidic strength and flake-like morphology of DGC-Me-SAPO-18 could retard the coke formation, leading to the prolonged catalytic lifetime.

Selective conversion of small bio-oxygenates into high quality gasoline precursors over deactivated ZSM-5 in MTG reaction

Selective conversion of two small bio-oxygenates (i-propanol and propanal) into high quality gasoline precursors over deactivated ZSM-5 in methanol to gasoline (MTG) reaction was investigated in this paper. The deactivated ZSM-5 catalyst exhibited a perfect catalytic performance and lifetime for converting i-propanol and propanal to branched olefin and/or oxygenates by oligomerization. NH3-TPD and FT-IR analyses indicated that the deactivated ZSM-5 catalyst still retained a mild acidity, which was strong enough for conversion of i-propanol and propanal due to their own high reactivity. An integration scheme of high quality and aromatic free bio-gasoline production with MTG process was thus proposed, requiring no additional investments on infrastructure and catalyst.

Methanol conversion to light olefins over surfactant-modified nanosized SAPO-34

Ultrasonic and microwave-assisted aging processes were employed in the static hydrothermal synthesis of nanosized SAPO-34 molecular sieve. A series of nanosized hierarchical SAPO-34 samples with different degrees of mesoporosity were utilized to investigate the impacts of mesoporosity on the catalytic performance of the methanol to olefins (MTO) reaction. The so-called series were synthesized in the presence of various mesogenous templates, such as TPOAC, CTAB, and their combinations. These SAPO-34 samples were characterized by XRD, FE-SEM, BET, FT-IR and NH3-TPD techniques. The catalytic activities were studied in a fixed-bed reactor under atmospheric pressure, 450 °C and WHSV of 4 h−1. Comprehending the results, it can be said that in comparison with the typical catalysts, reliable MTO catalytic lifetime (420 min) as well as sufficiently high light olefins selectivity (90 %) was obtained through the nanosized hierarchical porous SAPO-34 templated with a mixture of 50 % CTAB and 50 % TPOAC. This achievement is associated to its effective combination of acidity and porosity.

One-pot hydrothermal synthesis of nanostructured ZrAPSO-34 powder: Effect of Zr-loading on physicochemical properties and catalytic performance in conversion of methanol to ethylene and propylene

Nanostructured ZrAPSO-34 catalyst was successfully synthesized via hydrothermal method and Zr isomorphously was substituted into the framework of SAPO-34. The effect of various Zr loadings on the physicochemical properties and catalytic performance was investigated. The structure of the synthesized catalysts was characterized using XRD, FESEM, EDX, BET, FTIR, NH3-TPD and DR-UV-Vis techniques. For samples with low Zr content, relative crystallinity increased and intact CHA structure produced. However, by further Zr loading, relative crystallinity strongly reduced. Acidity results confirmed that Zr incorporation led to increase in both acid sites concentration and strength. Characterization results confirmed the successful incorporation of Zr into SAPO-34 framework. ZrAPSO-34 and SAPO-34 catalysts were applied in methanol to olefins reaction. The Zr incorporation and Zr content have significant effects on the lifetime and product selectivity. For the samples with low Zr content, catalytic lifetime was prolonged compared to the sample synthesized without metal. However by increasing Zr loading, it was reduced and methane selectivity was increased.

Enhancement of catalytic properties and lifetime of nanostructured SAPO-34 by La isomorphous substitution and alteration of Si/Al ratio used in methanol conversion to light olefins

Methanol conversion to light olefins was investigated over SAPO-34 catalysts with La introduction exploring the effect of different Si/Al ratios.

A Palladium-Tin Modified Microband Electrode Array for Nitrate Determination

A microband electrode array modified with palladium-tin bimetallic composite has been developed for nitrate determination. The microband electrode array was fabricated by Micro Electro-Mechanical System (MEMS) technique. Palladium and tin were electrodeposited successively on the electrode, forming a double-layer structure. The effect of the Pd-Sn composite was investigated and its enhancement of catalytic activity and lifetime was revealed. The Pd-Sn modified electrode showed good linearity (R2 = 0.998) from 1 mg/L to 20 mg/L for nitrate determination with a sensitivity of 398 μA/(mg∙L−1∙cm2). The electrode exhibited a satisfying analytical performance after 60 days of storage, indicating a long lifetime. Good repeatability was also displayed by the Pd-Sn modified electrodes. The results provided an option for nitrate determination in water.

Structural Changes in Tungsten and Tantalum Wires in Catalytic Chemical Vapor Deposition Using 1,3-Disilacyclobutane

Metal wires (typically made of W or Ta) serve as catalysts to decompose the precursor gases to form reactive species in the technique of catalytic chemical vapor deposition. The reactions of these reactive species with the heated wire cause structural changes in the wire, which affect its catalytic properties and lifetime. Here, we report a systematic study on characterizing the structural changes in W and Ta wires when they are exposed to 1,3-disilacylobutane, a useful single-source precursor for SiC film deposition. We have shown that filament temperature, reaction time, and filament material are among the important factors in determining the nature of metal alloys formed. Formation of crystalline W2C, SiC, and W5Si3 (weak) was observed on W, whereas crystalline TaC, SiC, and Ta5Si3 (weak) were formed on Ta. While both filaments proved to form cubic crystalline 3C-SiC at low temperatures, alloying has taken different paths at higher temperatures. Between 1400 and 2400 °C, alloying in W was dominated by the formation of W2C with little contribution from WC. For Ta, the main alloy formed was TaC in the temperature range of 1400–2000 °C. Heating the aged Ta filament to temperatures higher than 2000 °C tended to recover the metal wire. This same practice does not seem to work for W wires since more W2C is formed at high temperatures. It is concluded that Ta outperforms W for SiC film growth in its resistance to forming more carbides and its ability to recover at high temperatures.

Development of the CON-type Aluminosilicate Zeolite and Its Catalytic Application for the MTO Reaction

The CON-type aluminosilicate zeolites, which consist of a three-dimensional pore system with 12-, 12-, and 10-membered ring pores have been prepared by postsynthesis and the newly developed direct-synthesis methods. We first found that the CON-type aluminosilicate zeolites exhibited a higher catalytic performance in the methanol to olefins (MTO) reaction in terms of duration and propene selectivity than the MFI and *BEA-type aluminosilicate zeolites. They exhibited high propene selectivity, low ethene selectivity, and a very long catalytic life compared to Beta and ZSM-5; the selectivity for C3–C4 olefins reached 80%. Interestingly, the CON-type aluminosilicate zeolite synthesized by the direct-synthesis method showed a much longer catalytic lifetime than the one obtained by the postsynthesis method. The 27Al MAS and 27Al MQMAS NMR spectra suggest that there is a significant difference in the state of tetrahedrally coordinated Al species between the directly and postsynthesized zeolites, leading to the ma...

Hydrogen generation from the hydrolysis of sodium borohydride using chemically modified multiwalled carbon nanotubes with pyridinium based ionic liquid and decorated with highly dispersed Mn nanoparticles

Multiwalled carbon nanotubes (MWCNTs)/Ionic liquid (IL)/Mn nanohybrids are synthesized and their catalytic activity is examined for hydrogen generation from the hydrolysis of sodium borohydride (NaBH4). Transmission electron microscopy reveals that Mn nanoparticles well-distributed on the MWCNTs surface. Energy dispersive x-ray spectrometer and x-ray photoelectron spectroscopy confirms the presence of Mn and Ni atom in the nanohybrids. The nanohybrids exhibit excellent catalytic lifetime and gives the total turnover number of 18496 mol H2/mol catalyst in the hydrolysis of NaBH4, which can be attributed to the presence of Mn atom and IL containing nickel halide anion. It is worthy of note that a very small amount of catalyst is used for this hydrolysis reaction. The activation energy is found to be 40.8 kJ/mol by MWCNTs/IL/Mn nanohybrids from the kinetic study of the hydrogen generation from the hydrolysis of NaBH4. The improved hydrogen generation rate, lower activation energy, and less expensive make the nanohybrids promising candidate as catalyst for the hydrogen generation from NaBH4 solution. The nanohybrids are easy to prepare, store and yet catalytically active. The recycling process is very simple and further purification is not tedious.

CoAPSO-34 촉매상에서 DTO (Dimethyl Ether to Olefins) 반응에 미치는 Co/Al 및 Si/Al 몰 비의 영향

Abstract Effects of Co/Al and Si/Al molar ratios of cobalt incorporated SAPO-34 catalysts (CoAPSO-34) on their catalytic lifetime were investigated in dimethyl to olefin (DTO) reaction. The property of CoAPSO-34 catalysts was characterized using XRD, SEM, 29 Si MAS NMR, and NH 3 -TPD techniques. First, the lifetime of CoAPSO-34 prepared by varying Co/Al molar ratios was improved than that of using the SAPO-34 catalyst, and the optimal Co/Al molar ratio was 0.0025. The total acid site amounts increased from 0.432 to 1.111 mmol/g with increasing Si/Al molar ratios from 0.05 to 0.20 while fixing a Co/Al molar ratio of 0.0025. However, the catalysts with too high acid site amounts were deactivated rapidly with blockages of the pores due to the fast accumulation of polycyclic aromatic hydrocarbons in the cage. Therefore, the CoAPSO-34 catalyst with a proper Si/Al molar ratio of 0.10 was the most superior in terms of the lifetime, which was improved by about 87% as compared with that of the SAPO-34 catalyst.

DTO 반응에서 촉매수명과 경질 올레핀 선택도에 미치는 SAPO-34의 산 처리 효과

Effects of the post-acid treatment of SAPO-34 sample by hydrochloric acid were investigated to enhance the catalytic performance in DTO reaction. Uniformly sized SAPO-34 samples with cubic-like morphology were prepared by hydrothermal method using TEAOH and DEA as the structure directing agents. It was modified in terms of the HCl concentration and treating time. As a result, the total surface area and micropore volume for the well modified samples increased and the total acid site was somewhat decreased along with the erosion of the external surface. Especially, the catalytic lifetime and light olefins selectivity for acid treated SAPO-0.2 M (3 h) samples were considerably enhanced compared with those of untreated SAPO-34 samples. It indicates that the deactivation by coke formation proceeds mainly at the pore entrance on the external surface. Therefore, the acid treatment was confirmed to be a simple method which can significantly improve the catalytic performance by modifying the external surface of SAPO-34 catalyst.

Effect of cerium and zirconium nanoparticles on the structure and catalytic performance of SAPO-34 in steam cracking of naphtha to light olefins

The effects of cerium and zirconium nanoparticles and their interaction on the structure and catalytic performance of SAPO-34 were investigated in steam catalytic cracking to produce ethylene and propylene from naphtha. The prepared catalysts were characterized by means of XRD, FT-IR, BET, SEM and NH3-TPD techniques. The NH3-TPD results showed that the addition of cerium resulted in the increase of both weak and strong acid sites. However, zirconium addition diminished the weak acid sites and boosted the strong acid sites. The activity measurements indicated that modified catalysts possessing moderate acidity favored ethylene and propylene yield. Response surface methodology in combination with the central composite design was employed to statistically evaluate the effect of cerium (2–8 wt%) and zirconium (2–5 wt%) loading as well as finding an optimum catalyst. By using the desirability function, the optimum SAPO-34 which maximizes the yield of ethylene and propylene simultaneously was found at cerium loading of 2.92 wt% and zirconium loading of 2.98 wt%. Deactivation of SAPO-34 and optimized SAPO-34 were investigated for 10 h of time-on-stream. It was found that the catalytic lifetime of SAPO-34 was poor, but the optimized SAPO-34 showed better resistance to deactivation.

Additive explanation for anti-wear

Tribology Additives in oil are vital for protecting engines from wear by forming films at sliding interfaces. Zinc dialkydithiophosphate (ZDDP) has been used for decades to reduce engine wear. Now there is a strong incentive for finding a replacement for ZDDP: Its breakdown products shorten catalytic converter lifetime. Gosvami et al. examined exactly how ZDDP produces an anti-wear film under high stress or elevated temperature (see the Perspective by Schwarz). Understanding these mechanisms will help in the development of higher-performance and more effective additives. Science , this issue p. [102][1]; see also p. [40][2] [1]: /lookup/volpage/348/102?iss=6230 [2]: /lookup/doi/10.1126/science.aaa3276

Influence of temperature and space velocity on the MTO reaction over nano sheet-like SAPO-34 catalyst and the theoretical calculation

Nano sheet-like silicoaluminophosphate molecular sieve SAPO-34 was synthesized under hydrothermal conditions by using tetraethylammonium hydroxide as the template. The catalytic performances of methanol-to- olefin (MTO) reactions over nano SAPO-34 catalysts under different temperatures and weight hourly space velocity (WHSV) were systematically studied. The catalytic temperature and WHSV can affect both the catalytic lifetime and the selectivity of ethylene and propylene. The lifetime of catalyst decreased with the increase of catalytic temperature and WHSV. In addition, the ratio between ethylene and propylene enhanced with the increase of catalytic temperature, but decreased with the increase of WHSV. Density functional theory (DFT) calculations demonstrated that the energy barrier of producing ethylene is higher than that of propylene. According to the variation of Gibbs free energy along with temperature, the increase of temperature is more advantageous to the generation of ethylene.

Catalytic conversion of methanol to propylene over high-silica mesoporous ZSM-5 zeolites prepared by different combinations of mesogenous templates

The effects of mesoporosity on catalytic performance of methanol to propylene (MTP) reaction have been investigated by using a series of high-silica nanosized hierarchical ZSM-5 zeolites with different degrees of mesoporosity, which were hydrothermally synthesized in the presence of different mesogenous templates, i.e., TPOAC, CTAB, and their combinations. The results were compared with a conventional microporous ZSM-5 catalyst. The prepared catalysts were characterized by XRD, FE-SEM, BET, NH3-TPD and FT-IR techniques. Meanwhile, their catalytic activities were evaluated in a fixed-bed reactor under atmospheric pressure, 460 °C and WHSV of 1h−1. Compared with conventional catalyst, the nanosized hierarchical porous ZSM-5 templated with a mixture of 75% TPOAC and 25% CTAB displayed reliable MTP catalytic lifetime (76 h) as well as sufficiently high propylene selectivity (43.65%) and propylene to ethylene (P/E) ratio (4.05), which were predominately attributed to its optimal combination of acidity and porosity.

Improved Catalytic Lifetime of H2SO4 for Isobutane Alkylation with Trace Amount of Ionic Liquids Buffer

Trace amounts of ionic liquids have been mixed in sulfuric acid to enhance the catalytic performance for the alkylation of isobutane with butene. The experimental results from batch reactors indicated that the reaction efficiency was significantly improved. The effective catalytic lifetime of concentrated H2SO4 mixed with [Bmim][SbF6] was twice compared with pure H2SO4. Under the optimal conditions, the alkylate research octane (RON) reached 98, and the selectivity of C8 was 90%. The ionic liquids with SbF6 anion worked similar to buffer agents, which were in favor of keeping the acid strength of catalytic system, slowing the growth of acid soluble oil, and reducing acid consumption. In conclusion, the new catalytic system of acid and trace amounts of ionic liquids is very promising to substitute the old catalytic system of concentrated H2SO4 alone for the alkylation.

ZSM-5 Zeolite with Micro-Mesoporous Structures Synthesized Using Different Templates for Methanol to Propylene Reaction

ZSM-5 zeolites with different pore structures were synthesized using different templates(tetrapropyl ammonium hydroxide(TPAOH), cetyltrimethylammonium bromide(CTAB) and C18-6-6Br2). The obtained nanosized(NZ), mesoporous(MZ), and nanosheets(NSZ) ZSM-5 samples were compared with conventional microporous ZSM-5 zeolite(CZ). The physicochemical properties of these samples were characterized using X-ray diffraction(XRD), scanning electron microscopy(SEM), N2 adsorption-desorption,and temperature-programmed desorption of ammonia(NH3-TPD). The results showed that the mesopore volumes and surface areas of the four samples increased in the order NSZ MZ NZ CZ, and the ratio of strong/weak acidity increased in the order CZ MZ NZ NSZ. In the methanol to propylene(MTP) reaction,the catalyst porosity played an important role on the product selectivity and catalytic stability. The selectivities for propylene and total olefins improved with increasing mesoporosity; NSZ, with the largest mesopore volume, gave the highest propylene selectivity, i.e., 47.5%, and 78.4% total olefins. Meanwhile, the introduction of mesopores into the ZSM-5 zeolite extended the catalytic lifetime. The NZ sample displayed reliable MTP catalytic activity for 200 h, which was predominately attributed to its optimal combination of acidity and porosity.