The surface of transitional aluminas: A critical review

Fast pyrolysis oil from lignocellulosic biomass is an attractive energy carrier. However, to improve the product characteristics such as a reduced polarity and higher thermal stability, upgrading is required. We here report activities on the catalytic hydrotreatment of fast pyrolysis oil using bimetallic NiCu/delta-Al(2)o(3) catalysts with various Ni/Cu ratios (0.32 to 8.1 w/w) at a fixed total metal intake of about 20 wt% with the objective to improve product properties for co-feeding applications in conventional oil refineries. Hydrotreatment reactions were initially carried out for a model compound (anisole, continuous set-up, 300 degrees C, 10 bar) and subsequently for fast pyrolysis oil (batch autoclave, 1 h at 150 degrees C followed by 3h at 350 degrees C, at 100 bar initial pressure). Best results, i.e. the highest hydrodeoxygenation yield for experiments with anisole (75 mol%), and an upgraded oil with the most favorable properties for fast pyrolysis oil (high H/C ratio, low M-W of 500 g/mol, low thermogravimetric residue of 6.8 wt%), were obtained for a catalyst with a Ni to Cu wt% ratio of eight (16Ni2Cu). For this catalyst, hydrogen consumption was the highest (146 NL/kg(PO)). The findings were rationalized using a reaction network model earlier developed for Ru/C. Analysis of catalyst (ICP, HRTEM, XRD and TGA) before and after reaction showed the occurrence of leaching of both active metals (Ni and Cu) and support, as well as coke deposition on the support. The most active catalyst in the series (16Ni2Cu) also gave lowest leaching and coking levels in the series. (C) 2012 Elsevier B.V. All rights reserved.

Catalytic hydrotreatment of fast-pyrolysis oil using non-sulfided bimetallic Ni-Cu catalysts on a delta-Al2O3 support

Because of ultralow thermal conductivity, excellent catalytic activity, and better heat resistance than silica aerogel, alumina-based aerogel has drawn great interest as thermal insulators and catalysts. However, it is too fragile and sinters above 1000 °C (it shrinks drastically, >50%, and leaves the surface area as low as 10–70 m2/g at 1300 °C), which badly limits its high-temperature applications. Herein, super heat-resistant, strong alumina aerogels are prepared via a novel acetone-aniline in situ water formation (ISWF) method combined with novel modification techniques: supercritical fluid modification (SCFM) and hexamethyldisilazane gas phase modification. The heat resistance of alumina aerogel is enhanced up to 1300 °C via this method. The shrinkage of the optimized alumina aerogel is reduced to as low as 1 and 5% and the corresponding surface area reaches up to 152–261 and 125–136 m2/g after being heated to 1200 and 1300 °C for 2 h, respectively. The strength is significantly increased by more tha...

Nanoengineering Super Heat-Resistant, Strong Alumina Aerogels

This work is an original example to compare the results obtained after calcination of Al2O3 hydroxides and oxidation of alumino-formers alloys. FTIR and XPS signatures were obtained for various oxidation temperatures and compared with those known from the literature about calcination of Al2O3 precursors. The aim of this work is to evaluate the use of IR spectroscopy and XPS analysis to probe the structural varieties of Al2O3. For this objective, a study of the PM2000 oxidation at various temperatures was conducted by means of XRD, IR spectroscopy, XPS analysis, EDX analysis, and SEM observations. This allowed us to clearly differentiate the transition Al2O3 from the α-Al2O3 and, amongst the transition Al2O3, to differentiate the characteristic of the IR spectrum of γ-δ phases from that of the θ phase.

https://downloads.hindawi.com/journals/jspec/2015/868109.pdf

XPS, FTIR, EDX, and XRD Analysis of Al2O3 Scales Grown on PM2000 Alloy

In this work, we studied the aptitude to sintering green bodies using γ-Al 2 O 3 transition alumina as raw powder. We focused on the influence of the heating rate on densification and microstructural evolution. Phase transformations from transition alumina γ → δ → θ → α-Al 2 O 3 were studied by in situ X-rays diffraction from the ambient to 1200 °C. XRD patterns revealed coexistence of various phase transformations during the heating cycle. DTA and dilatometry results showed that low heating rate leads to a significant reduction of the temperature of the α-Al 2 O 3 alumina formation. Around 1190, 1217 and 1240 °C were found when using 5, 10 and 20 °C/min of heating rate, respectively. The activation energy for θ-Al 2 O 3  → α-Al 2 O 3 transformation calculated by Kissinger and JMA equations using dilatometry method were 464.29 and 488.79 kJ/mol, respectively and by DTA method were 450.72 and 475.49 kJ/mol, respectively. In addition, the sintering of the green bodies with low heating rate promotes the rearrangement of the grains during θ-Al 2 O 3  → α-Al 2 O 3 transformation, enhancing the relative density to 95% and preventing the development of a vermicular structure.

P. Berthet

Papers

Transition alumina phases induced by heat treatment of boehmite: An X-ray diffraction and infrared spectroscopy study