◇◇新语丝(www.xys.org)(xys.dxiong.com)(xys.3322.org)(xys.xlogit.com)◇◇ 石峰博士的纳米金制备法有疑问 作者:深秋十月 方先生: 您好!   近日看了新语丝上关于兰州化物所石峰博士的学术论文的讨论,不免好奇于 如何制备纳米金。比较石峰的制备法[1]和其他报道后,我发现石峰的制备法中 并无任何对还原步骤的描述。   在其他报道中,固态附载的金盐或氢氧化物以如下方法还原为零价的金属金: 1。氢气氛围中加热还原[2,3];2。煅烧还原[4];3。甲酸钠还原[4];4。甲醛 还原[4]。具体见下。   我由此认为石峰博士的纳米金制备法有疑问。按其方法制备的催化剂不太可 能含有纳米金颗粒。希望这只是单纯写作问题,但作为学术论文,这仍是不可原 谅的疏忽。 Literature Methods for Preparation of Nanogold Catalysts [1] Shi, F. et al, J. Am. Chem. Soc. 2005, 127, 4182-4183; Supporting Information Preparation of Au/poly: polymer immobilized Au catalysts, Au/poly, was prepared as follows: 2g of dried polymers (ca. φ0.5 mm, Amberlite IRA-400 (poly1), Shandong Dongda Chemical Industry Company, Zibo, 255200, China) was pretreated with 2M NaOH solution for 6 hours, and then filtrated and washed by distilled waster for 3 times (10ml×3). After drying at 80 for 3 hours, the ionexchanger was dipped in 0.001~0.006M solution of HAuCl4?4H2O and dried at 150 for 6 hours, and polymer supported nano-gold catalysts named 0.01wt%Au/Poly1, 0.05wt%Au/Poly1, 0.1wt%Au/Poly1 and 0.5wt%Au/Poly1 were obtained. The gold contents were 0.01wt%, 0.05wt%, 0.1wt% and 0.5wt% respectively. Using Amberlite IR-120 (poly 2) to instead of poly1, another catalyst named 0.05wt%Au/Poly2 was prepared. It was worth to note that the procedure for preparation of the catalysts had great effect on the catalytic activity and some unclear factors usually affected the catalytic activity severely. [2] Mohr, C. et al, J. Am. Chem. Soc. 2003, 125, 1905-1911; Experimental Section Gold particles were deposited on ZnO (EGA Chemie, Germany) by a conventional impregnation procedure. An appropriate volume of the gold precursor HAuCl4 was dissolved in water, and the resulting solution was brought into contact with the ZnO powder. This was followed by drying at 383 K for 2 h and subsequently reducing in a flow of hydrogen at 573 K for 3 h, resulting in a sample named Au/ZnO. [3] Mohr, C. et al, J. Catal. 2002, 213, 86-94; Experimental To ZrO2 (Aldrich), gold was applied as Au(OH)3 through precipitation from tetrachloroauric acid (HAuCl4, ALFA) with NH4OH. Various samples were repared, differing just by precipitation at different pH values of the aqueous solution. The resulting samples are named Au/ZrO2-DP22 (pH 5), Au/ZrO2-DP23 (pH 6), and Au/ZrO2-DP24 (pH 9). This precipitation step was followed by washing and filtering, drying of the precipitation product (393 K), calcination (3 h, 573 K, air, 5 l h?1), and reduction (573 K, H2, 5 lh?1). The standard reduction time was 3 h, variations from this treatment are indicated in the text. In these cases, the conditions of hydrogen treatment are included in the sample names. [4] Prati, L. et al, J. Catal. 1998, 176, 552; Experimental Gold catalysts were prepared using a HAuCl4 0.1 M solution obtained by dissolving 1.97 g of gold powder in a minimum amount of a 3 : 1 (v/v) mixture of concentrated HCl and HNO3 and then diluted to 100 ml with distilled water. After reduction all the catalysts were filtered and then washed with hot water until the filtrate was chloride free (AgCl test). The catalysts were used in wet form. 2.2.1. Gold on alumina. 1%Au on Al2O3 was prepared by using either incipient wetness impregnation (see below) or a deposition– precipitation method previously reported (8). The reduction step was performed by calcinating the catalyst at 623 K for 3 h in air. 2.2.2. Gold on carbon. (a) Incipient wetness impregnation. The support (2 g) was impregnated with 1 ml of 0.1M HAuCl4 diluted with distilled water to a volume equal to its pore volume. The suspension was mixed for 20 min and then added to a hot solution of HCOONa (20 ml of water and 200 mg of sodium formate). (b) Deposition–precipitation method. The solution of HAuCl4 0.1M(1 ml) was diluted with distilled water (10 ml) and a saturated solution of Na2CO3 was added until a fixed pH of 10 was reached. Then the mixture was added to a stirred slurry of carbon (2 g) in distilled water (20 ml). The slurry was allowed to stand for 1 h and then heated to 343K and reduced by adding HCHO 37% (1.5 ml) dropwise. On carbon support we have some evidence that the carbon itself acts as the reductant. In fact a catalyst prepared without adding HCHO is already active (although to in a minor extent) and contains all the gold added (ICP analysis). The HCHO is added to ensure a complete reduction of gold. (XYS20051222) ◇◇新语丝(www.xys.org)(xys.dxiong.com)(xys.3322.org)(xys.xlogit.com)◇◇