Impregnation precursors

V (2 ), Cr ( ), Zr (1 ), or Ta (1 ). The role of these promoters in the air cathode is unclear, and some have suggested that the active catalysts are alloys of the Ft with the transition metal (1,4) which form during heat-treatment of the oxide impregnated precursor. In the first section of this paper, we review the work from the Lawrence Berkeley Laboratory on the study of the mechanism of promotion of air cathode performance by these transition metal additives. 

H2Cl Pt to get non-chlorinated and chlorinated materials (labelled hereafter as N and Cl-samples) with metal loading of 3% Rh and 6% Pt (e.g. 300 pmol/g or ca. 1.5 atoms/nm ). The impregnated precursors were dried in air at 423K for 24 h. and then calcined at 673K in a 100 ml min dry air flow for 4 h. and finally stored in a desiccator luitil their use. BET surface areas were 91 2 m g for all four samples. 

A major effort was launched in the late 1980s to find a base metal additive capable of raising the selectivity of Pt for the conversion of SOF. Several oxides were able to lower SO2 oxidation activity, as measured by the temperature required to achieve 50% conversion. Vanadia and chromia (added by impregnating precursor salts onto Pt/alumina) raised T50 by 218 and 165°C respectively. Many other oxides, including those of Zr, Mn and Ti, raised T50, but by a much smaller amount (75°C or less). In addition to suppressing SO2 oxidation, the promoted catalysts had to show retained activity for SOF conversion. Laboratory studies used CO, propene and decane as surrogates for SOF. Here, results were mixed, with vanadia performing well with CO and propene but poorly with decane. 

Xp is about 0.35 (g ). The optimum temperature of conformation is 100 °C. No carbon disks were prepared for the KOH impregnated precursor because of the small effect of this chemical on the pyrolysis stage. 

Promoters are sometimes added to the vanadium phosphoms oxide (VPO) catalyst during synthesis (129,130) to increase its overall activity and/or selectivity. Promoters may be added during formation of the catalyst precursor (VOHPO O.5H2O), or impregnated onto the surface of the precursor before transformation into its activated phase. They ate thought to play a twofold stmctural role in the catalyst (130). First, promoters facilitate transformation of the catalyst precursor into the desired vanadium phosphoms oxide active phase, while decreasing the amount of nonselective VPO phases in the catalyst. The second role of promoters is to participate in formation of a soHd solution which controls the activity of the catalyst. 

Methods of preparation of the laminates depend on the partieular grade of polyimide resin used but in one process the polyimide precursor is dissolved in acetone and this solution is used to impregnate the glass or carbon fibre and thus produce a pre-preg . The pre-preg is dried and then pre-cured at about 200°C for about 3 hours. This operation reduces the volatile content and also modifies the flow properties to make them more suitable for the subsequent... 

Sulfur can replace 30-50% of the asphalt in the hlends used for road construction. Road surfaces made from asphalt-sulfur hlends have nearly double the strength of conventional pavement, and it has been claimed that such roads are more resistant to climatic conditions. The impregnation of concrete with molten sulfur is another potential large sulfur use. Concretes impregnated with sulfur have better tensile strength and corrosion resistance than conventional concretes. Sulfur is also used to produce phosphorous pentasulfide, a precursor for zinc dithiophosphates used as corrosion inhibitors. 

Usually noble metal NPs highly dispersed on metal oxide supports are prepared by impregnation method. Metal oxide supports are suspended in the aqueous solution of nitrates or chlorides of the corresponding noble metals. After immersion for several hours to one day, water solvent is evaporated and dried overnight to obtain precursor (nitrates or chlorides) crystals fixed on the metal oxide support surfaces. Subsequently, the dried precursors are calcined in air to transform into noble metal oxides on the support surfaces. Finally, noble metal oxides are reduced in a stream containing hydrogen. This method is simple and reproducible in preparing supported noble metal catalysts. 

A 20 wt% of Co/TiOa was prepared by the incipient wetness impregnation. A designed amoimt of cobalt nitrate [Co(N03) 6H20] was dissolved in deionized water and then impregnated onto TiOj containing various ratios of rutileianatase obtained from above. The catalyst precursor was dried at 110°C for 12 h and calcined in air at 500°C for 4 h. 

In this work, various conditions have been used for preparing catalysts to screening out a proper one mainly for CTA hydrogenation. The palladium precursor, impregnation time, calcination and reduction will be taken into account. 

Two most firequently applied palladium precursor, H2PdCl4 and Pd(NH3)4Cl2, were usrf to prepare Pd/CNF by west impregnation. Results of foe CTA hydrogenation showed that under the same palladium loading ratio (0.5Pd%, see Table 2), foe Pd/CNF fi-om H2PdCl4... 

Preparation conditions of Pd/CNFs by wet impregnation method, such as palladium precursor, impregnation time, calcinations and reduction, are proved to have profound effect on the catalytic property. The catalyst prqjared by impregnating HzPdCLi precursor in an hour, then calcinated in air and reduced in 20%H2/Ar is believed to perform better in CTA hydropurification than the industrial Pd/C under laboratory conditions. 

By loading pre-existing support materials in the form of shaped bodies with the catalytically active phase by means of impregnation or precipitation from solution. This is the preferred method when catalyst precursors are expensive and the aim is to deposit the catalytically active phase in the form of nanometre-sized particles on the support. All noble metal catalysts are manufactured in this way. 

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