A. O. S. Silva

Synthesis, characterization and catalytic application of cerium-modified MCM-41

The nanostructured CeMCM-41 material was synthesized by the hydrothermal method, using cethyltrimethylammonium bromide as template. The sample was characterized by X-ray diffraction, energy-disperse X-ray, thermogravimetry, nitrogen adsorption isotherm and pore size distribution. The specific surface area of CeMCM-41 was equivalent to 850 m 2 g -1 , with the pore width and mesopore volume of 3.8 nm and 0.8 cm 3 g -1 , respectively. To evaluate the catalytic performance of the CeMCM-41, a mass of ca. 0.1 g was heated from room temperature up to 723 K at heating hate of 10°C min -1 using oxygen flowing at 50 ml min -1 . The CeMCM-41 was tested as catalyst for n-heptane oxidation, in a fixed-bed continuous-flow reactor, at 723 K and F/W ratio (molar flow of reactant per mass of catalyst) of 0.4-0.6 g h mol -1 . The obtained products were analyzed in a gas chromatograph coupled to a mass spectrometer. The GC-MS analysis revealed that the main oxidation products obtained were typically CO and CO 2 , with 12% of hydrocarbon conversion.

Hydrothermal synthesis of cerium aluminophosphate

Abstract Cerium(III) aluminophosphate molecular sieve has been synthesized starting from aluminum hydroxide, phosphoric acid, hydrated cerium chloride and water, in the presence of a di-isopropylamine organic template. This material has a tetrahedral framework of aluminum (AlO 2 ) − and phosphorus (PO 2 ) + . The obtained structure was similar to that of ALPO-11. The materials have been characterized by using various physicochemical methods. The incorporation of Ce(III) ions into the aluminophosphate matrix did not change the ALPO-11 structure, but did, however, increase the surface area and total acidity.

Kinetic Parameters of Polyethylene Degradation by the Natural Zeolite Chabazite

High-density polyethylene (PE) was subjected to thermal degradation alone and in the presence of an ammonium-exchanged zeolite chabazite (CHA/PE). The processes were carried out in a reactor connected online to a gas chromatograph/mass spectrometer in order to analyse the evolved products. Polymer degradation was also evaluated by thermogravimetry, from room temperature up to 800°C, under a dynamic nitrogen atmosphere, with multiple heating rates. From the TG curves, the activation energy relating to the degradation process was calculated by using the Flynn and Wall multiple heating rate kinetic model for pure PE and for CHA/PE. The exchanged chabazite exhibited good selectivity for the catalytic degradation of PE to low molecular mass hydrocarbons.

m-Xylene Isomerization in SAPO-11/HZSM-5 Mixed Catalyst

The catalytic isomerization of m-xylene was studied over a solid acid silicoaluminophosphate type SAPO-11, mixed to HZSM-5 zeolite. The reaction was processed varying the temperature and weight hourly space velocity, using a fixed bed continuous flow reactor. The m-xylene suffers isomerization to p-xylene and o-xylene by molecular displacement of methyl groups. The mixed catalyst was selective to p-xylene at 623 K and 2.5 h−1 with a maximum p/o ratio of 2.05. The ethylbenzene formation was not observed in the products. In this process an apparent activation energy of the order of 13.9 kJ mol−1 was obtained.

Hydrothermal synthesis and thermal characterization of niobium-aluminophosphate with AEL structure ☆

Abstract Niobium-aluminophosphate materials with AEL structure (NbALPO-11) were prepared by hydrothermal method, using pseudoboehmite, phosphoric acid, hydrated niobium oxalate, water and di-isopropylamine. The obtained materials were characterized by X-ray fluorescence, X-ray diffraction, infrared spectroscopy, scanning electron microscopy, thermogravimetry and measurements of acidity. From the X-ray diffraction it was confirmed that niobium was incorporated in the framework at low Nb concentration. The obtained NbALPO-11 presented acidity of weak and medium strength, as verified by n -butylamine desorption. The characterization of the catalytic active sites was carried out by isopropanol dehydration at a temperature of 400°C, and space velocities of 1.6, 3.2, 4.8, 6.4 and 8.0 h −1 . The materials were active for this process where the main products were propene and di-isopropyl ether.

Hydrodesulfurization of thiophene over coblat and molybdenum sulfides supported on MCM-41 materials

In this work was studied the potential application of molybdenum suphides supported on SiMCM-41 and A1MCM-41 materials in the thiophene hydrodesulfurization. The SiMCM-41 and AIMCM-41 materials were synthesized by hydrothermal method using cethyltrimethylammonium bromide as template. The deposition of the active HDS species was performed by solvent excess impregnation of ammonium tetrathiomolybdate salt over the supports followed by calcination. Cobalt was used as promoter in order to obtain a Co/(Co+Mo) atomic ratio of 0.3. The materials presented activity in thiophene HDS.

Fischer-Tropsch synthesis over Co/SiMCM-41 and Co/SiO2 materials: The role of support at different cobalt loadings

The conversion of synthesis gas to liquid products via Fischer-Tropsch synthesis (FTS) is an important process in the generation of clean fuels of sulfur and nitrogen compounds. Catalysts based on iron are very used in the conventional process due its cheap manufacture price. Recently the use of cobalt as promoter gave good results. In this work are presented new alternatives for FTS with the use of cobalt supported on molecular sieves of the type MCM-41. A comparative study with the usual catalysts based on silica was accomplished with different levels of cobalt.

Catalytic cracking of C5+ gasoline over hy zeolite

The catalytic conversion of a C5+ natural gasoline over the HY zeolite has been studied. The results show the formation of C2, C3 and C4 hydrocarbons with an apparent activation energy of ca. 39 kJ mol-1.

Synthesis, Characterization and Catalytic Properties of NBALPO-11

Niobium containing aluminophosphate materials with AEL structure were prepared by the hydrothermal method. The chemical composition of the hydrogel was: 1 DIPA: 1 Al2O3: (1-x) P2O5: x Nb2O5: 80 H2O, with x=0.025, 0.050, 0.075 and 0.100. The crystallization was carried out at temperature of 170°C for 72 h. The materials obtained were characterized by XRF, DRX, FTIR, TG and measurements of acidity. The characterization of the catalytic active sites were carried out in the isopropanol dehydration at temperature of 400°C, and WHSV of 1.6, 3.2, 4.8, 6.4 and 8.0 h-1 . The samples showed good catalytic activity with selectivity to propene.

Hydrothermal synthesis and crystallographic properties of silicoaluminophosphate with different content of silicon

Abstract Silicoaluminophosphate molecular sieves of SAPO-11 type were synthesized with variation in the [Si/(Al + Si + P)] ratio, using the hydrothermal method, starting from silica, pseudobohemite, orthophosphoric acid and water, in the presence of a di-isopropylamine organic template. The samples were characterized by elemental analysis, X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG/DTA), and scanning electron microscopy (SEM). The incorporation of silicon into the framework of SAPO-11 is demonstrated by the variation of the unit-cell volume with the silicon content. CELREF software was used to index and refine the main lines of the XRD patterns. It is shown that the unit-cell volume decreases over a wide range of silicon content.