Research on the Acidity of the Double-function Catalyst for DME Synthesis from Syngas

Two kinds of HZSM-5 zeolite (SiO₂/Al₂O₃ = 50,300) were introduced into the STD (syngas-to-DME) reaction and the double-function catalysts containing CuO/ZnO/Al₂O₃ and HZSM-5 were investigated by activity evaluation and NH₃-TPD. It was found that the acidity of HZSM-5 played a critical role in the performance of STD catalyst, and an appropriate acidic amount was required to obtain the best activity of STD catalyst; more and less acidic amount were both unfavorable for DME yield.     

Skeletal isomerization of 1-butene over ferrierite and ZSM-5 zeolites: influence of zeolite acidity

Three ferrierite (FER) and five ZSM-5 (MFI) zeolites with SiO₂Al₂O₃ ratio ranging from 27 to 2000 are tested as catalysts for the skeletal isomerization of 1-butene at 350–450°C and atmospheric total pressure in order to study the influence of acidity and pore structure of zeolite on conversion and selectivity. The catalytic and NH₃ temperature-programmed desorption results from FER and MFI catalysts with the same SiO₂/Al₂O₃ ratio reveal that the pore structure of FER zeolite rather than its acidity may play an important role in achieving high selectivity for the skeletal isomerization of 1-butene to isobutene.     

Effects of preparation methods for V<Subscript>2</Subscript>O<Subscript>5</Subscript>-TiO<Subscript>2</Subscript> aerogel catalysts on the selective catalytic reduction of NO with NH<Subscript>3</Subscript>

A series of V₂O₅-TiO₂ aerogel catalysts were prepared by the sol-gel method with subsequent supercritical drying with CO₂. The main variables in the sol-gel method were the amounts of V₂O₅ and when the vanadium precursor was introduced. V₂O₅-TiO₂ xerogel and V₂O₅/TiO₂ (P-25) were also prepared for comparison. The V₂O₅-TiO₂ aerogel catalysts showed much higher surface areas and total pore volumes than V₂O₅-TiO₂ xerogel and impregnated V₂O₅/TiO₂ (P-25) catalysts. The catalysts were characterized by N₂ physisorption, X-ray diffraction (XRD), FT-Raman spectroscopy, temperature-programmed reduction with H₂ (H₂-TPR), and temperature-programmed desorption of ammonia (NH₃-TPD). The selective catalytic reduction of NOx with ammonia in the presence of excess O₂ was studied over these catalysts. Among various V₂O₅-TiO₂ catalysts, V₂O₅ supported on aerogel TiO₂ showed a wide temperature window exhibiting high NOx conversions. This superior catalytic activity is closely related to the large amounts of strong acidic sites as well as the surface vanadium species with characteristics such as easy reducibility and monomeric and polymeric vanadia surface species. This work was presented at the 7 ^th Korea-China Workshop on Clean Energy Technology held at Taiyuan, Shanxi, China, June 26–28, 2008.     

Dehydrogenation of isobutane over Sn/Pt/Na-ZSM-5 catalysts: The effect of SiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> ratio,amount and distribution of Pt nanoparticles on the catalytic behavior

Sn/Pt/Na-ZSM-5 was used as catalyst for the dehydrogenation of isobutane, and the effect of SiO₂/Al₂O₃ ratio and the dispersion of Pt nanoparticles on the conversion and product selectivity were studied under atmospheric pressure at 848 K. The catalysts were characterized by various techniques such as H₂ chemisorption, TEM, SEM, EDX, XRD, FT-IR, TG/DTG, elemental analysis by XRF and ICP techniques. Higher dispersion of Pt nanoparticles in the catalyst with SiO₂/Al₂O₃ ratio of 40 resulted in higher selectivity for isobutene.     

Alkali-treatment of ZSM-5 zeolites with different SiO2/Al2O3 ratios and light olefin production by heavy oil cracking

Four kinds of ZSM-5 zeolites with different SiO₂/Al₂O₃ ratios are alkali-treated in 0.2 M NaOH solution for 300 min at 363 K. Changes to the compositions, morphologies, pore sizes, and distributions of the zeolites are compared before and after alkali-treatment. The changes observed are largely influenced by the SiO₂/Al₂O₃ ratios with which the zeolites are synthesized. A possible mechanism of desilication during alkali-treatment is proposed. The SiO₂/Al₂O₃ ratio of zeolites is found to influence the yield of light olefins that use heavy oil as feedstock. Alkali-treated ZSM-5 zeolites produce higher yields of light olefins compared to either untreated zeolites or the industry catalyst CEP-1. It is believed that alkali-treatment introduces mesopores to the zeolites and improves their catalytic cracking ability. ZSM-5 zeolites with SiO₂/Al₂O₃ ratios of 50 also present superior selectivity toward light olefins because of their optimized hierarchical pores.     

Characterization of Pd catalysts supported on USY zeolites with different SiO2/Al2O3 ratios for the hydrogenation of naphthalene in the presence of benzothiophene

A series of ultra-stable Y-type (USY) zeolites with different SiO₂/Al₂O₃ ratios in the range of 10–80 were used as supports for preparing Pd/USY at 2 wt% Pd loading. The FT-IR of hydroxyl groups of USY zeolites, the n-butylamine chemisorption and the temperature-programmed desorption were used in combination to characterize the zeolite acidity. TPR, H₂-TPD and chemisorption using H₂ were used to characterize the Pd reduction and dispersion. The hydrogenation of naphthalene was conducted at 200 °C in the presence of benzothiophene at different sulfur/metal ratios. The hydrogenation activity, selectivity, and the sulfur tolerance strongly depended on the SiO₂/Al₂O₃ ratio (thus the acidity) of the zeolites. The activity decreased with increasing SiO₂/Al₂O₃ in this range. The IR and n-butylamine TPD showed that both the amount and strength of Brönsted acidity decreased with the increase of the SiO₂/Al₂O₃ ratio. The good relationship between the acidity modification and catalytic performance suggests that the sulfur tolerance of Pd/USY zeolite might be due to the desired metal-support interaction, which resulted in larger amount of electron-deficient Pd. However, as shown in TGA and TPO-IR studies, the higher hydrogenation performance on more acidic zeolite also caused higher amount of carbonaceous species on the catalyst.     

CrHZSM-5 Zeolites – Highly Efficient Catalysts for Catalytic Cracking of Isobutane to Produce Light Olefins

The CrHZSM-5 catalysts with trace amount of Cr were firstly used for catalytic cracking of isobutane, and the effect of Cr-loading on the catalytic performances of CrHZSM-5 catalysts for the cracking of isobutane was also studied. The results suggested that when the loading of Cr in the CrHZSM-5 catalysts was less than 0.038 mmol/g Cr, especially at Cr loading of 0.004 mmol/g, both the reactivity of isobutane cracking and the selectivity to light olefins of CrHZSM-5 samples were greatly enhanced compared with the unpromoted HZSM-5, and very high yields of olefins(C₂+C₃) and ethylene were obtained. For instance, the yield of olefins(C₂+C₃) and ethylene reached 56.1% and 30.8%, respectively, at 625 °C when 0.004 mmol/g Cr was loaded on HZSM-5 sample.     

Polystyrene-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite solid polymer electrolyte for lithium secondary battery

In a common salt-in-polymer electrolyte, a polymer which has polar groups in the molecular chain is necessary because the polar groups dissolve lithium salt and coordinate cations. Based on the above point of view, polystyrene [PS] that has nonpolar groups is not suitable for the polymer matrix. However, in this PS-based composite polymer-in-salt system, the transport of cations is not by segmental motion but by ion-hopping through a lithium percolation path made of high content lithium salt. Moreover, Al₂O₃ can dissolve salt, instead of polar groups of polymer matrix, by the Lewis acid-base interactions between the surface group of Al₂O₃ and salt. Notably, the maximum enhancement of ionic conductivity is found in acidic Al₂O₃ compared with neutral and basic Al₂O₃ arising from the increase of free ion fraction by dissociation of salt. It was revealed that PS-Al₂O₃ composite solid polymer electrolyte containing 70 wt.% salt and 10 wt.% acidic Al₂O₃ showed the highest ionic conductivity of 9.78 × 10^-5 Scm^-1 at room temperature.     

Performance of Ni catalyst supported on La-hexaaluminate in CO<Subscript>2</Subscript> reforming of CH<Subscript>4</Subscript>

CO₂ reforming of CH₄ was performed using Ni catalyst supported on La-hexaaluminate which has been an well-known material for high-temperature combustion. La-hexaaluminate was synthesized by sol-gel method at various conditions where different amount of Ni (5–20 wt%) was loaded. Ni/La-hexaaluminate experienced 72 h reaction and its catalytic activity was compared with that of Ni/Al₂O₃, Ni/La-hexaaluminate shows higher reforming activity and resistance to coke deposition compared to the Ni/Al₂O₃ model catalyst. Coke deposition increases proportionally to Ni content. Consequently, Ni(5)/La-hexaaluminate(700) is the most efficient catalyst among various Ni/La-hexaaluminate catalysts regarding the cost of Ni in Ni(X)/La-hexaaluminate catalysts. BET surface area, XRD, EA, TGA and TPO were performed for surface characterization. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Characterization of Fischer–Tropsch Cobalt-Based Catalytic Systems (Co/SiO<Subscript>2</Subscript> and Co/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>) by X-ray Diffraction and Magnetic Measurements

Results of the characterization of six Co-based Fischer–Tropsch (FT) catalysts, with 15% Co loading and supported on SiO₂ and Al₂O₃, are presented. Room temperature X-ray diffraction (XRD), temperature and magnetic field (H) variation of the magnetization (M), and low-temperature (5 K) electron magnetic resonance (EMR) are used for determining the electronic states (Co⁰, CoO, Co₃O₄, Co²⁺) of cobalt. Performance of these catalysts for FT synthesis is tested at reaction temperature of 240 °C and pressure of 20 bars. Under these conditions, 15% Co/SiO₂ catalysts yield higher CO and syngas conversions with higher methane selectivity than 15% Co/Al₂O₃ catalysts. Conversely the Al₂O₃ supported catalysts gave much higher selectivity towards olefins than Co/SiO₂. These results yield the correlation that the presence of Co₃O₄ yield higher methane selectivity whereas the presence of Co²⁺ species yields lower methane selectivity but higher olefin selectivity. The activities and selectivities are found to be stable for 55 h on-stream.     

Infrared and raman characterization of V<Subscript>2</Subscript>O<Subscript>5</Subscript> on zirconia modified with WO<Subscript>3</Subscript> and activity for acid catalysis

Vanadium oxide supported on zirconia modified with WO₃ was prepared by adding Zr(OH)₄ powder into a mixed aqueous solution of ammonium metavanadate and ammonium metatungstate followed by drying and calcining at high temperatures. The characterization of prepared catalysts was performed by using FTIR, Raman, and XRD. In the case of calcination temperature at 773 K, for samples containing low loading V₂O₅ below 18 wt%, vanadium oxide was in a highly dispersed state, while for samples containing high loading V₂O₅ equal to or above 18 wt%, vanadium oxide was well crystallized due to the high V₂O₅ loading on the surface of ZrO₂. The ZrV₂O₇ compound was formed through the reaction of V₂O₅ and ZrO₂ at 873 K, and the compound decomposed into V₂O₅ and ZrO₂ at 1,073 K, these results were confirmed by FTIR and XRD. Catalytic tests for 2-propanol dehydration and cumene dealkylation have shown that the addition of WO₃ to V₂O₅/ZrO₂ enhanced both catalytic activity and acidity of V₂O₅-WO₃/ZrO₂ catalysts. The variations in catalytic activities for both reactions are roughly correlated with the changes of acidity.     

Enhanced Stability of HZSM-5 Supported Ga2O3 Catalyst in Propane Dehydrogenation by Dealumination

Gallium oxide catalysts supported on HZSM-5 with different Si/Al ratios were characterized by pyridine adsorption FT-IR, model reactions and XPS studies. As the Si/Al ratio of the support HZSM-5 zeolite rises, the acidity of the supported catalysts decreases accordingly, which comes from two aspects: the loss of acid sites present on HZSM-5 support and the loss of the acid sites present on gallium oxides. The latter was caused by the change in the interaction between Ga₂O₃ and support. The initial activity in the propane dehydrogenation decreases with increasing Si/Al ratio while the stability increases. The enhanced stability is thought to be caused by the decrease of the acidity of the catalysts, resulting in the suppression of the side reactions, such as cracking and oligomerization.     

Vapor phase reaction of cyclohexanone oxime over boria modified HSZM-5 zeolites

The vapor phase Beckmann rearrangement of cyclohexanone oxime has been carried out over zeolites and boria modified HZSM-5 zeolites to elucidate the effects of acidity and acid strength distribution on the conversion and ε-caprolactam selectivity. Although ε-caprolactam selectivity was increased with the SiO₂Al²O³ ratio in a HZSM-5 zeolite, the highest selectivity in the study was accomplished over a boria modified HZSM-5. The selectivity was dependent on the ratio of weak acid sites to strong acid sites. The boria played an important role in controlling the acid strength distribution of the zeolites. It was found that the production of a polymer over strong acid sites caused a decrease in ε-caprolactam selectivity during the reaction.     

Surface Acidity of H-Beta and Its Catalytic Activity for Alkylation of Benzene with Propylene

The acidity of H-beta zeolites with SiO₂/Al₂O₃ ratios ranging from 20 to 350 was characterized by NH₃-TPD profiles and FTIR spectra of adsorbed pyridine. As SiO₂/Al₂O₃ ratios of the H-beta zeolites increased, NH₃-TPD acidic amount of the samples is decreased. The IR bands of the adsorbed pyridine on the zeolites are also decreased with the increased SiO₂/Al₂O₃ ratios. The batch reaction of propylene and benzene was carried out in liquid phase at 423 K over H-beta zeolites. The selectivity to isopropylbenzene was high. The catalytic activity of H-beta zeolites is in direct proportion to the acidic amount of the zeolites in general. H-beta zeolite of SiO₂/Al₂O₃=27, which contains the highest amount of Brønsted acid sites as indicated by FTIR spectra of adsorbed pyridine, is the most reactive catalyst in the alkylation reaction. In continuous liquid-phase reactions, high propylene conversion and isopropylbenzene selectivity can be achieved at 413–453 K with benzene to propylene mole ratio from 4 to 8. The catalytic activity and selectivity of the H-beta zeolite do not change after 1100 h of reaction.     

Maximization of total surface area of Pt-SnO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst by the Taguchi method

The maximization of the total surface area of Pt-SnO₂/Al₂O₃ catalyst was studied by using the Taguchi method of experimental design. The catalysts were prepared by sol-gel method. The effects of HNO₃, H₂O and aluminum nitrate concentrations and the stirring rate on the total surface area were studied at three levels of each. L₉ orthogonal array leading nine experiments was used in the experimental design. The parameter levels that give maximum total surface area were determined and experimentally verified. In the range of conditions studied it was found that, medium levels of HNO₃ and H₂O concentration and lower levels of aluminum nitrate concentration and stirring rate maximize the total surface area.     

Synergism Between Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Au/TiO<Subscript>2</Subscript> in the Low Temperature Oxidation of Propene

CO impedes the low temperature (<170 °C) oxidation of C₃H₆ on supported Pt. Supported Au catalysts are very effective in the removal of CO by oxidation, although it has little propene oxidation activity under these conditions. Addition of Au/TiO₂ to Pt/Al₂O₃ either as a physical mixture or as a pre-catalyst removes the CO and lowers the light-off temperature (T ₅₀) for C₃H₆ oxidation compared with Pt catalyst alone by ~54 °C in a feed of 1% CO, 400 ppm C₃H₆, 14% O₂, 2% H₂O.     

Shape-selective methylation of 2-methylnaphthalene with methanol over hydrothermal treated HZSM-5 zeolite catalysts

Shape-selective methylation of 2-methylnaphthalene (2-MN) was carried out over hydrothermally treated HZSM-5 (SiO₂/Al₂O₃=83) zeolite catalysts under a fixed-bed down-flow reactor, methanol and 1,3,5-trimethylbenzene (TMB) were used as methylating agent and solvent, respectively. The results show that hydrothermal treatment improves the selectivity to 2,6-dimethylnaphthalene (2,6-DMN) and the stability. HZSM-5 catalyst hydrothermally treated at 550 °C followed by acid leaching exhibits 7.1% of 2,6-DMN yield after 5 h time on stream (TOS), and 13.4% of 2-MN conversion with the 2,6-/2,7-DMN ratio of 1.8 after 8 h of TOS.     

Effect of the zeolite modulus of Pt/MOR/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts on the <Emphasis Type="Italic">n</Emphasis>-heptane isomerization reaction

The effect of the mordenite acidic modulus (SiO₂/Al₂O₃, 20 and 30) of Pt/MOR/Al2O3 catalysts on the heptane isomerization reaction is investigated. The content of zeolite in the catalysts is varied from 10 to 50 wt %, with platinum applied to the samples from solutions of different precursors: H₂PtCl₆ and [Pt(NH₃)₄]Cl₂. It is established via the TPD of ammonia and FTIR spectroscopy (the adsorption of NH₃ and СО) that the total acidity of zeolite falls as the modulus grows: the number of Brønsted (BAC) and Lewis (LAC) acidic sites is reduced, accompanied by an increase in the strength of their acidity. The catalysts are tested in the n-heptane isomerization reaction. It is shown that the selectivity of n-heptane isomerization falls substantially when the acidic mordenite modulus is increased from 20 to 30.     

Synthesis of ZSM-5 type zeolites with and without template and evaluation of physicochemical properties and aniline alkylation activity

ZSM-5 zeolite containing SiO₂/Al₂O₃ = 28 was synthesised by hydrothermal process with and without template. Characterisation of the zeolites was done using XRD, IR, NMR, SEM and BET surface area measurements. Acidity of the zeolites was measured by ammonia adsorption-desorption. Catalytic activity of HZSM-5 zeolites was evaluated by aniline alkylation, cumene dealkylation, alkylation of benzene with ethylene and propylene and isomerisation ofm-xylene. Catalytic activity is discussed from the point of view of zeolite acidity and morphology.     

How oxide carriers affect the reactivity of V2O5 catalysts in the oxidative dehydrogenation of propane

The catalytic pattern of several oxide carriers (MgO, Al₂O₃, ZrO₂, TiO₂, SiO₂, HY zeolite) and supported V₂O₅ (4.7–5.3 wt%) catalysts in the oxidative dehydrogenation of propane to propylene (PODH) has been comparatively investigated. The fundamental role of the oxide support on both reducibility and reactivity of vanadia catalysts has been assessed. A direct relationship between the specific surface activity of oxide carriers and that of vanadia catalysts is discussed. The inverse relationship between the specific activity and the onset temperature of reduction marks the prevailing redox behaviour of V₂O₅ catalysts in the PODH reaction. This revised version was published online in July 2006 with corrections to the Cover Date.