The chemical nature of carbonaceous deposits and their role in methane dehydro-aromatization on Mo/MCM-22 catalysts

Various carbonaceous deposits are formed during the course of methane dehydro-aromatization (MDA) under non-oxidative conditions on Mo/MCM-22 catalysts. These carbon species were investigated by various temperature-programmed techniques such as TPH and TPCO2, combining with TPO and TGA results in order to reveal their chemical nature and determine their amounts. The TPO profiles recorded from coked Mo/MCM-22 catalysts show two temperature peaks: one at about 756 K and the other at about 876 K. The coke amounts related to these two peaks were determined on the basis of the corresponding corrected and deconvoluted TPO profiles, combining with the TGA profiles concerned.

Study of the carbonaceous deposits formed on a Mo/HZSM-5 catalyst in methane dehydro-aromatization by using TG and temperature-programmed techniques

Carbonaceous deposits formed during the temperature-programmed surface reaction (TPSR) of methane dehydro-aromatization (MDA) over Mo/HZSM-5 catalysts have been investigated by TPH, TPCO2 and TPO, in combination with thermal gravimetric analysis (TG). The TPO profiles of the coked catalyst after TPSR of MDA show two temperature peaks: one is at about 776 K and the other at about 865 K. The succeeding TPH experiments only resulted in the diminishing of the area of the high-temperature peak, and had no effect on the area of the low-temperature peak. On the other hand, the TPO profiles of the coked catalyst after succeeding TPCO2 experiments exhibited obvious reduction in the areas of both the high-and low-temperature peaks, particularly in the area of the low-temperature peak. On the basis of TPSR, TPR and TPCO2 experiments and the corresponding TG analysis, quantitative analysis of the coke and the kinetics of its burning-off process have been studied. (C) 2001 Elsevier Science B.V. All rights reserved.

Titanium species in titanium silicalite TS-1 prepared by hydrothermal method

The titanium species existing in titanium silicalite TS-1, which is prepared by hydrothermal method, were investigated using chemical analysis, XRD, FT-IR, Si-29 MAS NMR, UV-VIS, ESR. It has been observed that several kinds of titanium species may exist in titanium silicalite. The form that titanium atoms incorporate into the framework of titanium silicalite synthesized using tetrapropylammonium bromide (TPABr) as template differs from that using the classical method. But, the symmetry of titanium silicalite, changes from monoclinic to orthorhombic with the increase of titanium content in both methods. The Ti-O-2(-) originated from framework titanium and H2O2 has the moderate stability and may be active site in oxidation reaction. TS-1 synthesized using TPABr as template does not contain anatase, but contains a kind of partly condensed titanium species with six-fold coordination. The titanium species may correspond to 270-280 mn band in UV-VIS spectra and also can form Ti-O-2(-). But, this kind of Ti-O-2(-) is very stable and cannot be catalytic active site. So, the six-fold coordination titanium species may be inactive in both the oxidation reaction and the decomposition of H2O2. The hypothesis has been further proved by the phenomena that the titanium species is easily washed off using acid, and acid treating will not influence the catalytic performance of TS-1. (C) 2001 Elsevier Science B.V. All rights reserved.

Hydrothermal synthesis of alumina nanotubes templated by anionic surfactant

The alumina nanotubes were prepared by using the anionic surfactant, sodium dodecyl sulfonate (SDS), as structure-directing template for the first time with Al(NO3)(3)center dot 9H(2)O as precursor via a hydrothermal method. Structure and morphology of the nanotubes were characterized by XRD, TEM, FT-IR, TG and N-2 adsorption-desorption. The obtained nanotubes were found having outer diameters from 6 to 8 nm with length up to 200 nm. (C) 2005 Elsevier B.V. All rights reserved.