| 1. |
- Aguilar-Mamani, Wilson, et al.
(författare)
-
Internal structure of a gel leading to NBA-ZSM-5 single crystals
- 2018
-
Ingår i: Journal of porous materials. - : Springer. - 1380-2224 .- 1573-4854. ; 25:6, s. 1551-1559
-
Tidskriftsartikel (refereegranskat)abstract
- Porous gel structures are formed during the synthesis of the zeolite ZSM-5 due to the reaction between a source of aluminosilicate, sodium hydroxide, water and a structure directing agent, such as e.g. tetrapropylammonium (TPA) or n-butylamine (NBA). In the present work, the formation of the gel in a heterogeneous system leading to the crystallization of NBA-ZSM-5 zeolite from leached metakaolin was studied extensively. The solid and liquid phases obtained after separation were analyzed by inductively coupled plasma sector field mass spectrometry, dynamic light scattering, extreme high resolution-scanning electron microscopy, energy dispersive spectroscopy, high resolution-transmission electron microscopy, X-ray diffraction and nitrogen gas adsorption. The main gel phase formed after hydrothermal treatment exhibited a sponge-like structure resembling those forming in (Na, TPA)-ZSM-5-based systems. For the first time, the walls of the main gel were shown to be inhomogenous and to possess a biphasic internal structure consisting of a mesoporous skeleton of aluminosilicate nanoparticles embedded in a silicate-rich soluble matrix of soft matter. The data presented in this paper is of primary importance to understand the mechanism by which the gel is consumed and contributes to the growth process of the zeolite crystals.
|
|
| 2. |
- Ajaikumar, Samikannu, et al.
(författare)
-
Transesterification of diethyl malonate with n-butanol over HPWA/MCM-41 molecular sieves
- 2013
-
Ingår i: Journal of porous materials. - Dordrecht : Springer. - 1380-2224 .- 1573-4854. ; 20:4, s. 951-959
-
Tidskriftsartikel (refereegranskat)abstract
- Mesoporous Si-MCM-41 and Al-MCM-41 (Si/Al = 100) materials were synthesized via a hydrothermal method. Three different ratios (10, 20 and 30 wt%) of heteropoly tungstic acid (HPWA) was loaded on Si-MCM-41 by wet impregnation techniques. The characteristic structural features of the prepared materials were studied by various physico-chemical techniques such as X-ray diffraction (XRD), Nitrogen physisorption (BET), temperature programmed desorption of ammonia (TPD) and transmission electron microscopy (TEM). Transesterification of diethyl malonate (DEM) with n-butanol under autogeneous conditions in a temperature range from 50 to 125 °C was selected as the test reaction for the as synthesized materials. The reactants were fed with various mole ratios in order to determine the optimal feed composition leading to maximum yields of transesterified products. The results indicated that the conversion of diethylmalonate depends on the HPWA concentration on the support, temperature, reaction time and mole ratio of the reactants. Further, the catalytic efficiency of HPWA/MCM-41 was compared with that of Al-MCM-41. The solid acid HPWA/MCM-41 catalysts have several advantages in comparison to conventional mineral acid catalysts which are heterogeneous, eco-friendly, highly active and selective in the formation of transesters.
|
|
| 3. |
- Andersson, Henrik, et al.
(författare)
-
Electroless deposition and silicidation of Ni contacts into p-type Porous Silicon
- 2008
-
Ingår i: Journal of porous materials. - : Springer Science and Business Media LLC. - 1380-2224 .- 1573-4854. ; 15:3, s. 335-341
-
Tidskriftsartikel (refereegranskat)abstract
- Porous Silicon (PS) has attracted much attention since the discovery of its photo luminescent behavior. It has also been used for various other applications such as electroluminescent light emitting-diodes (LEDs), photodetectors and solar cells. For such devices, it is important to make good metallic Ohmic contacts to the PS in order to maximize the efficiency. In order to produce buried contacts, barrier layers, Schottky devices, etc. in PS, it is advantageous to deposit metal that covers not only the surface of the porous layer, but also the inside walls and the bottom of the pores. In this work experiments were performed to examine the morphology and properties of electroless deposition of Nickel into p-type PS and subsequent formation of Nickel silicide after heat treatment. Circular PS samples of 6 mm diameter were produced by anodizing p-type Silicon wafers for 15 min and were subsequently plated with Ni using three different plating baths. The pores are on average 20 µm deep and 4 µm wide. Two samples of each type were heat treated in an nitrogen atmosphere for one hour at 400 and 600°C respectively to produce Nickel silicide. Reference samples were made by means of electron beam evaporation of Ni. SEM micrographs show that the best pore coverage was achieved using the Ni plating bath containing hypophosphite. I–V characterization shows that different rectifying and Ohmic contacts can be formed between electroless deposited Ni and PS depending on the conditions of the heat treatment. XRD and EDX characterizations show that both the NiSi and Ni2Si phases exist in the sample at the same time.
|
|
| 4. |
- Boström, Zebastian, 1983
(författare)
-
Nitration of anisol in dispersions of mesoporous oxides impregnated with heteropolyacids
- 2012
-
Ingår i: Journal of Porous Materials. - : Springer Science and Business Media LLC. - 1573-4854 .- 1380-2224. ; 19:5, s. 921-933
-
Tidskriftsartikel (refereegranskat)abstract
- Amorphous and long range ordered cubic and hexagonal silica impregnated with heteropolyacids was investigated as catalyst for nitration of anisol using HNO3 as nitrating agent. The use of HNO3 together with a solid acid catalyst is an environmentally attractive alternative to the conventional procedure that employs HNO3 together with H2SO4. The aqueous nitric acid was loaded in the pores of the mesoporous material and the HNO3 filled particles were subsequently dispersed in anisol. The reaction took place at the interface between the two liquid phases, i.e., at the pore openings. It was shown that ordered mesoporous silica is more efficient than amorphous silica and that silica with cubic geometry is the most efficient. Two heteropolyacids of Keggin type, phosphotungstic acid and phosphomolybdic acid, were tested. One Wells–Dawson type of phosphotungstic acid was included as well as cesium exchanged heteropolyacid acids of Keggin type. The best yield was obtained with mesoporous cubic silica impregnated with cesium exchanged phosphotungstic acid. The amount of heteropolyacid used in the impregnation turned out to be critical. Above a certain loading the activity went down, probably due to clogging of the pores. The preferred catalyst could also be reused with retained activity.
|
|
| 5. |
|
|
| 6. |
- Dyhr, Kurt, et al.
(författare)
-
Effects of zeolite addition on the manganese catalyzed decomposition of hydrogen peroxide
- 1999
-
Ingår i: Journal of porous materials. - 1380-2224 .- 1573-4854. ; 6:4, s. 275-282
-
Tidskriftsartikel (refereegranskat)abstract
- Manganese catalyzed decomposition of hydrogen peroxide in the presence of various zeolites was investigated at different pH values, Mn concentrations and zeolite: Mn ratios. Depending upon the level of these parameters the zeolites studied displayed both catalytic and inhibitive effects on the rate of decomposition. At a high pH (10.8) Mordenite 10A in a twofold excess on an ion-exchange capacity basis acted as an inhibitor whereas the other zeolites had little or no effect on the reaction rate. At a lower pH (9.0) zeolite A when added in large excess resulted in a remarkable inhibitive effect whereas the same zeolite resulted in a promotion of the catalytic action of manganese at an intermediate pH (9.9). The complex catalytic nature of zeolite-peroxide-Mn systems is discussed.
|
|
| 7. |
- Gevert, Börje Sten, 1956, et al.
(författare)
-
Preparation of discrete colloidal ZSM-5 crystals with high Al-content
- 2011
-
Ingår i: Journal of Porous Materials. - : Springer Science and Business Media LLC. - 1573-4854 .- 1380-2224. ; 18:6, s. 723-728
-
Tidskriftsartikel (refereegranskat)abstract
- A new method for synthesis of discrete colloidal ZSM-5 particles with SiO(2)/Al(2)O(3) M ratios as low as 30 and sizes .4-1 micrometer has been developed. The relation between the synthesis parameters and synthesis yield, crystal structure, crystallinity, particle size and morphology was investigated. The synthesis yield increases and the deviation of the SiO(2)/Al(2)O(3) ratio in the product from that in synthesis mixture decreases with increasing autoclave temperature suggesting that the introduction of aluminium into the zeolite structure is favoured by high autoclave temperature during the synthesis and that temperature determines the lower limit of the SiO(2)/Al(2)O(3) ratio. The SiO(2)/Al(2)O(3) ratio in the synthesis mixture decreases with autoclave temperature suggesting that the introduction of aluminium into the zeolite structure is favoured by high autoclave temperature during the synthesis and that the temperature determines the lower limit of SiO(2)/Al(2)O(3) ratio. Synthesis mixture, aimed to yield a high SiO(2)/Al(2)O(3) ratio, gives smaller zeolite crystals, higher specific surface areas, higher geometric areas (external surface area of the crystals) and a more oval crystal shape compared with lower ratios, synthesised at the same temperature. Higher autoclave temperature during the synthesis gives larger zeolite crystals and a more hexagonal crystal shape compared with zeolites synthesised at lower temperatures, for the same SiO(2)/Al(2)O(3) ratios.
|
|
| 8. |
- Gustafsson, Mikaela, 1980-, et al.
(författare)
-
Crystal Formation and Size Control of Zeolitic Imidazolate Frameworks with Mixed Imidazolate Linkers
- 2013
-
Ingår i: Journal of porous materials. - : Springer Science and Business Media LLC. - 1380-2224 .- 1573-4854. ; 20:1, s. 55-63
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of synthesis parameters, such as batch composition and synthesis temperature, on the formationand crystal size of zeolitic imidazolate frameworks(ZIFs) using mixed linkers, imidazole (Im) and benzimidazole(bIm), were studied by X-ray powder diffraction(XRPD) and scanning electron microscopy (SEM). ZIF-7and ZIF-62 were identified as the main phases and a phasediagram relating the batch composition and the finalproduct was constructed based on XRPD and SEM. Therange of batch composition giving rise to ZIF-7 and ZIF-62was identified from the phase diagram. Changes of crystalsize and morphology of ZIF-7 and ZIF-62 in terms of batchcomposition and synthesis temperature were studied bySEM and different trends were observed for the two ZIFs.Thermogravimetric analysis (TGA) and in situ XRPDshowed that ZIF-62 possesses a similar high thermal stabilityas ZIF-7.
|
|
| 9. |
- Hedlund, Jonas
(författare)
-
Control of the preferred orientation in MFI films synthesized by seeding
- 2000
-
Ingår i: Journal of porous materials. - 1380-2224 .- 1573-4854. ; 7:4, s. 455-464
-
Tidskriftsartikel (refereegranskat)abstract
- Single crystal silicon and quartz wafers were seeded with colloidal TPA-silicate-1 crystals. Hydrothermal treatment of the seeded substrates was used to grow dense MFI films. The preferred orientation of the crystals constituting the films as a function of the amount and size of seeds, film thickness and hydrothermal treatment conditions was investigated. In thin films, most of the crystalline material was found to be oriented with the b-axes close to perpendicular to the substrate surface. In thick films, the a- or c-axes were close to perpendicular to the substrate surface depending on the conditions used for hydrothermal treatment. The seed size and amount was found to affect the rate of change in preferred orientation as a function of film thickness. A film growth mechanism which is able to explain the experimental results is proposed
|
|
| 10. |
- Mintova, Svetlana, et al.
(författare)
-
Preparation of zeolite Y-vegetal fiber composite materials
- 1996
-
Ingår i: Journal of porous materials. - 1380-2224 .- 1573-4854. ; 3:3, s. 143-150
-
Tidskriftsartikel (refereegranskat)abstract
- Zeolite Y crystallization on chemi thermo mechanical pulp (CTMP) fluff, linen and cotton substrates using two different approaches for the deposition was studied. In the first approach a seed-film method was applied. This method involves surface charge modification of the substrates, adsorption of a monolayer of colloidal zeolite Y crystals onto the surfaces and subsequent growth of these colloidal zeolite crystals into a continuous zeolite film. Application of this method resulted in continuous films of zeolite Y on all substrates investigated. The second approach involved direct synthesis on substrates subjected to chemical or mechanical pretreatment in order to modify their surface properties. Chemical treatment was found to improve the crystallization on cotton and linen fibers but not so for the CTMP. Mechanical pretreatment enhanced the zeolite crystallization on the linen fibers but not on the other substrates. The zeolite Y-vegetal fiber composites were characterized by SEM, XRD, and thermal analysis.
|
|
