Aromatic chemicals by iron-catalyzed hydrotreatment of lignin pyrolysis vapor.

Lignin is a potential renewable material for the production of bio-sourced aromatic chemicals. We present the first hydrotreatment of lignin pyrolysis vapors, before any condensation, using inexpensive and sustainable iron-silica (Fe/SiO2 ) and iron-activated carbon (Fe/AC) catalysts. Lignin pyrolysis was conducted in a tubular reactor and vapors were injected in a fixed bed of catalysts (673 K, 1 bar) with stacks to investigate the profile of coke deposit. More than 170 GC-analyzable compounds were identified by GCxGC (heart cutting)/flame ionization detector mass spectrometry. Lignin oligomers were analyzed by very high resolution mass spectrometry, called the "petroleomic" method. They are trapped by the catalytic fixed bed and, in particular, by the AC. The catalysts showed a good selectivity for the hydrodeoxygenation of real lignin vapors to benzene, toluene, xylenes, phenol, cresols, and alkyl phenols. The spent catalysts were characterized by temperature-programmed oxidation, transmission electron microscopy (TEM), and N2 sorption. Micropores in the Fe/AC catalyst are completely plugged by coke deposits, whereas the mesoporous structure of Fe/SiO2 is unaffected. TEM images reveal two different types of coke deposit: 1) catalytic coke deposited in the vicinity of iron particles and 2) thermal coke (carbonaceous particles ≈1 µm in diameter) formed from the gas-phase growth of lignin oligomers.

Acetylene hydrogenation over Ni-Cu nanoparticles supported on silica prepared by aqueous hydrazine reduction.

Non conventional nickel (1%) and nickel (1%)-copper (0.2-0.75%) catalysts supported on silica, prepared by aqueous hydrazine reduction of nickel acetate at 70 degrees C, were studied in acetylene hydrogenation, mainly at 60 degrees C. The obtained results show that the metal dispersion decreases whereas the conversion passes through a maximum with increasing copper content. The reaction produces ethylene, benzene, ethane, n-butane, small amounts of higher hydrocarbons and a paraffinic product. Ethylene and benzene are rather low temperature products (below 80 degrees C) whereas the saturated hydrocarbons, mainly ethane, are rather formed at higher temperature. The presence of water in the feed gas changed the catalyst performances. The carbonaceous deposit during acetylene hydrogenation was studied by means of temperature programmed surface reaction (TPSR). Analysis of the results obtained showed that the changes observed in conversion/selectivity may be correlated with changes in Ni-Cu interactions, chemisorption equilibria or/and coke deposit. A comparative study of classical/non classical Ni/SiO2 catalysts is reported.

Study of support effects on the reduction of Ni2+ ions in aqueous hydrazine.

We have studied the effect of silica of quartz-type on the reducibility of nickel acetate in aqueous hydrazine (80 degrees C, pH = 10-12) and metal particle formation. The obtained materials were characterized by X-ray diffraction, transmission electron microscopy, and thermodesorption experiments. With nickel acetate alone, the reduction was partial (45%) and a metal film at the liquid-gas interface or a powdered metal precipitate with an average particle size of 120 nm was obtained. In the presence of silica as the surfactant, the reduction of nickel acetate was total and the nickel phase deposited as a film on the support with an average particle size of 25 nm. Supported nickel acetate was also totally reduced. Crystallites of a mean particle size of about 3 nm were obtained. Decreasing the nickel content or increasing the hydrazine/nickel ratio decreased the metal particle size. Whiskers were formed for low nickel loadings. Hydrogen thermal treatment of the reduced phase showed that the organic acetate fragment, belonging to the precursor salt, still remained strongly attached to the nickel phase. The amount of the retained organic matrix depended on the metal particle size. Surface defects are suggested as active sites, which enhanced nickel ion reduction in the presence of silica as the surfactant or support. Metal-support interactions and the nucleation/ growth rate were the main factors determining the size and morphology of the supported metal particles formed. The organic matrix covered the reduced nickel phase.