A cooperative effect between support and the heterogenised metalloporphyrins on electrocatalytic oxygen reduction

A new general method to heterogenise porphyrins and different metalloporphyrins (Co, Fe) on silica, mesoporous MCM-41 and delaminated zeolites ITQ-2 and ITQ-6 yields stable materials, which act as active catalysts for the electrochemical oxygen reduction, without catalyst desorption from the electrode.     

Acidity and porosity modulation of MWW type zeolites for Nopol production by Prins condensation

Prins condensation of β-pinene with paraformaldehyde was carried out over MCM-22, delaminated ITQ-2 and silica pillared MCM-36. The mesopore-containing MCM-36 and ITQ-2 catalysts exhibit higher conversion of β-pinene due to more exposed acid sites. Lewis acid sites are responsible for Prins condensation while Brønsted acid sites favor the isomerization of pinene. The Brønsted acid sites can be removed mostly by ion-exchanging the zeolites with sodium cations. Thus, NaMWW zeolites had a higher selectivity towards Nopol. Of these, NaITQ-2 showed the highest activity and selectivity, and is a stable and reusable catalyst for production of Nopol.     

Synthesis of ITQ-2 Zeolites and Catalytic Performance in n-Dodecane Cracking

ITQ-2 zeolites were prepared by sequential alkali-swelling and ultrasonic-delamination of precursor MCM-22 and characterized by X-ray powder diffraction, scanning electron microscopy, nitrogen adsorpti...     

Preparation of ITQ-29 (Al-free zeolite A) membranes

Membranes consisting of Al-free ITQ-29 (a zeolite with the LTA-type structure) have been prepared on alumina tubular supports by seeded liquid phase hydrothermal synthesis. A supramolecular organic structure-directing agent (SDA) was used for the synthesis of ITQ-29 that must be removed from the zeolite pores to activate the membrane for permeation. The high temperature needed to decompose SDA from small-pore zeolites could create thermal stresses that affect the final membrane quality. Because of this, the effect of the atmosphere (N₂, O₂, air and O₃/air) and temperature of the membrane calcination process has been studied. An ITQ-29 membrane activated by means of the combination of pyrolytic (at 723 K) and ozonization (at 473–573 K) treatments gave the best results, with N₂/CH₄ and N₂/propane selectivities well above the corresponding Knudsen values.     

Changing the hydroisomerization to hydrocracking ratio of long chain alkanes by varying the level of delamination in zeolitic (ITQ-6) materials

Several delaminated ITQ-6 acid samples have been synthesized and tested in the isomerization of n-hexadecane. It has been found that the swelling time is a decisive parameter to prepare ITQ-6 catalytic materials with different ratios of micro to mesoporous surface area. n-Hexadecane hydroisomerization results indicate that the appropriate control of the delamination conditions can drive to obtain optimized ITQ-6 materials highly active for the hydroisomerization/hydrocracking of long chain alkanes to produce lube oils, diesels or gasolines.     

Synthesis of acid–base bifunctional CaO/ITQ-2 zeolite catalyst for phosphorylation of dodecanol

A series of acid–base bifunctional CaO/ITQ-2 zeolite catalysts were prepared by introducing calcium into the ITQ-2 zeolite. The catalysts were characterized by X-ray diffraction, FT-IR, NH₃-TPD and CO₂-TPD. The characterization results proved that ITQ-2 zeolite was synthesized by delaminating the MCM-22 zeolite. After modification by CaO, the catalysts could simultaneously have alkaline and acidic sites with little structural change. We then studied the catalytic capabilities of the prepared catalysts in the phosphorylation of dodecanol to di-dodecyl phosphate (DAP). The results show that ITQ-2 catalyst has higher selectivity for DAP than MCM-22. Versus ITQ-2 zeolite, the CaO/ITQ-2 catalysts have excellent acid–base cooperativity. The conversion of phosphoric acid and the selectivity of di-dodecyl phosphate could reach 80.2% and 77.5%, respectively over 3 wt.%CaO/ITQ-2 at optimal conditions. The catalytic activity of CaO/ITQ-2 catalyst could be regenerated by roasting after four times of reusing.     

Study of the structure directing effect of the chiral cation (1S,2S)-2-hydroxymethyl-1-benzyl-1-methylpyrrolidinium in aluminosilicate preparations in the presence of co-structure directing agents

We explore the structure directing role of the chiral cation (1S,2S)-2-hydroxymethyl-1-benzyl-1-methylpyrrolidinium (SS-bmpm) in the synthesis of Al-containing zeolite materials in the presence of co-structure directing agents (co-SDAs). Three different co-SDAs are studied: tetramethylammonium (TMA), quinuclidine and sodium. Synthesis with TMA as co-SDA yields a ferrierite related phase and a material from the MWW family, where the SS-bmpm and the TMA cations are incorporated intact within the samples. Quinuclidine produces instead amorphous solids, while the use of Na⁺ leads to crystalline phases that crystallized as a result of the degradation of the SS-bmpm cation. A subsequent computational study based on molecular mechanics was performed in an attempt to unravel the location of TMA and SS-bmpm cations within the void space of the complex MWW structure. The results suggest that the sinusoidal channels are exclusively filled by TMA, while the bulky SS-bmpm cations can only be accommodated within the MWW super-cages, thus providing a new example of cooperative structure-directing effects of small and bulky cations in the synthesis of complex zeolite structures.     

MCM-22、MCM-49和MCM-56分子筛的表征

MWW结构分子筛是一类新型的催化材料,具有独特的10元环孔道和12元环孔穴结构、优良的水热稳定性和特殊的酸中心分布,在多种反应中表现出良好的催化活性。以六亚甲基亚胺为模板剂,合成了具有MWW结构的MCM-22、MCM-49和MCM-56三种分子筛,并采用XRD、BET、TG/DTG和SEM手段对合成分子筛进行了表征,表明它们具有相同的单层结构,彼此之间的区别只有层间排列的结合层度和结合方式不同。MCM-56是薄层结构,晶体的层数少,MCM-22和MCM-49是多层结构,层数多。MCM-22的层间结合比较疏松,MCM-49的层间结合比较紧密。     

Methanol synthesis over Pd/SiO2 with narrow Pd size distribution prepared by using MCM-41 as a support precursor

All silicious MCM-41 was investigated as a support or a support precursor for Pd/SiO₂ and prepared catalysts were tested for methanol synthesis from CO and H₂. The methods of Pd loading on the MCM-41 were impregnation, seed impregnation and chemical vapor deposition (CVD). For both impregnations, most Pd existed outside of the pore as large particles, and only a small part of Pd was inserted into the pore of MCM-41 retaining the initial structure. On the contrary, in the catalyst prepared by CVD method, the MCM-41 structure was completely destroyed to become amorphous SiO₂. Yet the average Pd particle size in this catalyst was smaller and its distribution was narrower than those of the catalysts prepared by impregnation methods. In the methanol synthesis from CO hydrogenation the catalyst prepared by CVD showed higher methanol selectivity than other MCM-41-derived catalysts. This result was considered to be due to the more uniform distribution of the Pd particle size.     

Characterization and catalytic properties of MCM-56 and MCM-22 zeolites

We present an investigation of the structure and properties of MCM-56 and MCM-22. These materials have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and N₂ adsorption isotherms. DIFFaX was used to simulate pronounced peak broadening in the X-ray diffraction patterns of MCM-56. Toluene disproportionation is used as a test reaction to compare the catalytic activity of MCM-22 and MCM-56. We have found that MCM-56 is made of very thin MWW-type layers. The layers are typically one unit cell along the c direction (with a few of them having two or three unit cells). These very thin layers of MCM-56 become tightly curled upon calcination. The structures thus formed pack very efficiently, and this phenomenon prevents access of organic molecules like toluene to most of the 12 MR cups on the crystal exterior. Although MCM-56 is active for the disproportionation of toluene, its activity is lower than that of MCM-22. A calcination procedure that prevents the curling up of the MCM-56 layers is needed to make MCM-56 a useful catalyst for large organic molecules.     

n-Pentane isomerization over promoted SZ/MCM-41 catalysts

With metal sulfate as the precursor, the catalysts of sulfated zirconia on MCM-41, Al- and Ga-promoted sulfated zirconia on MCM-41 (named as SZ/MCM-41, ASZ/MCM-41 and GSZ/MCM-41, respectively) were prepared by direct dispersion in the as-synthesized MCM-41 materials, followed by thermal decomposition. The catalysts were characterized with various techniques such as XRD, FTIR, N₂ adsorption, NH₃-TPD, DRIFT, and TPR-MS. The ordered porous structure was still maintained in the catalysts. The addition of promoters helps to retard the phase transformation of ZrO₂ from tetragonal phase to monoclinic phase. Isomerization of n-pentane was investigated over the catalysts. In comparison to SZ/MCM-41, both promoted catalysts showed much improved catalytic activity and selectivity for isomerization of n-pentane. Moreover, the catalytical activities of both promoted catalysts for pentane isomerization remained steady over the period of 180 min while the activities of the unpromoted catalyst decreased in <120 min. Characterization of acidity showed no significant difference in strength distributions of the acid sites over the catalysts. The nature of acid sites in SZ/MCM-41 was affected by the presence of aluminum, but not affected by the presence of gallium. On the other hand, TPR study shows sulfur on GSZ/MCM-41 is much easier to reduce than SZ/MCM-41 and ASZ/MCM-41. The presence of gallium improved the redox capability provided by the sulfate ions in GSZ/MCM-41 catalyst. The causes for the promotion effects of Ga and Al are discussed.     

Enhancement of the photocatalytic activity of pelletized TiO2 for the oxidation of propene at low concentration

In a previous study we have shown that the pelletization of titanium dioxide, a convenient step for gas phase applications, causes an important activity lost. Such activity lost can be partially recovered pelletizing in presence of carbon materials. Porosity, as well as carbon conductivity of the selected carbon material, is important. Based on these previous results, we analyze the pelletization of TiO₂ in presence of “white additives”, such as MCM-41, zeolites, metal–organic framework, SiO₂, Al₂O₃, glass wool and quartz wool. Our results show that the activities of these composite photocatalytic pellets are higher than that of 100% TiO₂-pellets. Pellets containing MCM-41, precipitated SiO₂, glass wool and quartz wool present the highest propene conversions. Attention has been paid to the effect of porosity and UV-absorbance on the resulting photocatalytic activity. Although it is difficult to find a correlation between the porosity of these “white additives” and the photocatalytic activity of the TiO₂-based materials, additives with no porosity or with some mesoporous contribution seem to be desired to maximize the activity. The different catalytic activities for the studied photocatalysts could not be explained on basis of their UV-absorption and further research is currently being performed trying to deep into the reasons for such behaviour. Comparison of the photocatalytic activities for pellets containing the above-mentioned “white additives” with those of a TiO₂/carbon photocatalyst having the highest porosity and conductivity among all those studied highlights the superior performance of the samples containing “white additives”.     

Synthesis of mesoporous carbon supports via liquid impregnation of polystyrene onto a MCM-48 silica template

Mesoporous MCM-48 was synthesised and used as a template to synthesise mesoporous carbon materials. Polystyrene, the carbon source, together with sulfuric acid and toluene were added to the template (160 °C for 6 h) and this procedure generated a low surface area carbon supported/MCM-48 material. A repeat addition and carbonisation step was needed to form the precursor carbon/MCM-48 material that was pyrolysed at 900 °C to generate graphitic mesoporous carbon materials, characterised by XRD, HR-TEM, Raman spectroscopy and surface area analysis. The effect of the amount of polystyrene as well as the role of the pyrolysis temperature on the final product was investigated. This synthesis methodology can readily be controlled to produce partially ordered graphitic mesoporous carbon supports with predictable pore width and surface area.     

Niobic acid and niobium phosphate as highly acidic viable catalysts in aqueous medium: Fructose dehydration reaction

All silicious MCM-41 was investigated as a support or a support precursor for Pd/SiO₂ and prepared catalysts were tested for methanol synthesis from CO and H₂. The methods of Pd loading on the MCM-41 were impregnation, seed impregnation and chemical vapor deposition (CVD). For both impregnations, most Pd existed outside of the pore as large particles, and only a small part of Pd was inserted into the pore of MCM-41 retaining the initial structure. On the contrary, in the catalyst prepared by CVD method, the MCM-41 structure was completely destroyed to become amorphous SiO₂. Yet the average Pd particle size in this catalyst was smaller and its distribution was narrower than those of the catalysts prepared by impregnation methods. In the methanol synthesis from CO hydrogenation the catalyst prepared by CVD showed higher methanol selectivity than other MCM-41-derived catalysts. This result was considered to be due to the more uniform distribution of the Pd particle size.     

Comparative catalytic studies on the conversion of 1-butene and n-butane to isobutene over MCM-22 and ITQ-2 zeolites

The catalytic properties of H-MCM-22 and Pt-MCM-22 for the skeletal isomerization of 1-butene and the dehydroisomerization of n-butane were compared with those obtained from their delaminated derivatives, H-ITQ-2 and Pt-ITQ-2. The overall results of our study strongly suggests that the desired 1-butene and n-butane conversions to isobutene in steady state occur mainly near the pore mouth inlets of the sinusoidal 10-ring channels retained in both of MCM-22 and ITQ-2 and inside this intralayer void space, respectively, which may be attributed to the unique geometric constraints imposed by the two-dimensionality of the pore system with a suitable degree of ellipticity of 10-ring channels. Whereas coke formation on the sinusoidal channels during the 1-butene skeletal isomerization can occur in such a way as to make most of the intrachannel Brønsted acid sites less available for nonselective dimerization-cracking reactions, it appears that the presence of H₂ in the n-butane dehydroisomerization stream would prevent extensive coke buildup, thereby allowing pore diffusion of reactants and products even in steady state.     

Ruthenium-containing MCM-22 and ITQ-2 as potential redox catalysts for benzhydrol oxidation

Journal of Porous Materials - About 5&nbsp;wt% of ruthenium (Ru) was incorporated on layered zeolite frameworks, such as MCM-22 and ITQ-2, using the incipient wetness method. The well-dispersed...     

Accelerated synthesis of all-silica DD3R and its performance in the separation of propylene/propane mixtures

Synthesis of the all-silica Deca-Dodecasil 3 Rhombohedral (DD3R) zeolite was accelerated 10 times by seeding with small amount of crystals (0.02 wt%) with yields approaching 100%. The effects of other synthesis variables, like silica source, the presence of methanol or the synthesis pH on the final product distribution have been studied. The adsorption and separation of propylene and propane mixtures on this material are presented. The improved synthesis may form the basis to scale-up production of DD3R for selective separation processes. The single component adsorption isotherms could be well described with a dual-site Langmuir model. The binary mixture adsorption was determined from breakthrough/desorption experiments at 323, 358 and 383 K. By modelling the adsorptive column, diffusion coefficients at infinite dilution for single component and the effect of propane over propylene adsorption were determined. Cylindrical geometry describes the pore topology of DDR type materials well. Propane decreases the uptake rate of propylene by adsorption in the surface of the crystals. Propylene diffusion is best described by the “strong confinement” model inside the zeolite cages. Separation is due to only propylene adsorption with diffusion as rate determining step.Results revealed DD3R as a very effective molecular sieve for the separation or purification of propane–propylene mixtures.     

均三甲苯在MCM-22和MCM-56分子筛上的吸附和扩散

以MCM-22和MCM-56分子筛为研究对象,考察烃类均三甲苯在MWW型分子筛上的吸附和扩散,同时对分子筛进行XRD、N2吸附和TEM等表征,探究分子筛的结构特性与吸附和扩散之间的关系。研究表明,均三甲苯在MWW型分子筛中的吸附和扩散位置为外表面半超笼。单层和错层结构使MCM-56较MCM-22分子筛拥有更多的外表面酸性位,有利于均三甲苯的吸附。与MCM-22相比,MCM-56分子筛片层结构较薄,焙烧导致晶体外部结构的卷曲使烃类大分子均三甲苯在MCM-56分子筛中的扩散受阻。     

Cerium-containing MCM-41 materials as selective acylation and alkylation catalysts

The synthesis of Ce–MCM-41, Al–MCM-41 and Ce–Al–MCM-41-type mesoporous materials was carried out hydrothermally by refluxing the gel with magnetic stirring under atmospheric pressure for 24–36 h. The samples were characterized thoroughly in order to obtain the structural and textural properties, which reveal the presence of well-ordered M41S-type materials. The Ce–MCM-41 samples were used for catalytic acylation of alcohols, thiols, phenols and amines show good activity and selectivity including high chemoselectivity towards selective monofunctional acylation of bifunctional compounds. Quite importantly the acylation of bulky molecules such as cholesterol, ergesterol and β-sitosterol could be achieved using Ce–MCM-41 as solid catalyst. The presence of Ce along with Al in Ce–Al–MCM-41 was found to have synergistic effect as Ce–Al–MCM-41samples were more active catalysts for alkylation of naphthalene compared to either Ce–MCM-41 or Al–MCM-41 with comparable Si/Al or Si/Ce molar ratio.     

PFG NMR self-diffusion of propylene in ITQ-29, CaA and NaCaA: Window size and cation effects

Pulsed field gradient (PFG) nuclear magnetic resonance (NMR) spectroscopy was used to measure and rationalize the self-diffusion coefficients of propylene in various LTA materials having different framework composition and varying proportions of charge balancing cations: ITQ-29 (Si/Al = ∞), CaA (Si/Al = 1), and six NaCaA (Si/Al = 1) samples at greater than 50% Na⁺ exchange. The critical role of the framework Si/Al ratio on the self-diffusivity of propylene is demonstrated. Changes in self-diffusion driven by changes in framework composition are well documented in the literature. Diffusion frequency response experiments in the pure silica and alumino-phosphate forms of the CHA structure are included in this work to illustrate such situation.For the LTA structures, propylene was chosen as a very sensitive probe molecule because its size is comparable to the size of the 8-ring window apertures in the materials. A clear increase in self-diffusivity with the size of the window apertures, which increases with Al content in the framework, is shown. Thus, ITQ-29 and CaA exhibit the lowest and highest self-diffusivities, respectively. The self-diffusivities in the NaCaA samples lie in between those of ITQ-29 and CaA and increase with the Ca²⁺ content. Thus, the presence of extra-framework balancing cations in either CaA or NaCaA does not lead to lower self-diffusivities than in the cation-free ITQ-29. The lower self-diffusivities in ITQ-29, instead, can be largely attributed to its smaller window size, which is a more dominant effect than any reduction in self-diffusivity caused by the cations, at the levels of Na⁺ exchange studied.