Chemical Engineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK.
Nanotechnology. 2012 Jul 27;23(29):294002. doi: 10.1088/0957-4484/23/29/294002. Epub 2012 Jun 28.
Catalytic hydrodechlorination (HDC) is an effective means of detoxifying chlorinated waste. Gold nanoparticles supported on Fe(3)O(4) have been tested in the gas phase (1 atm, 423 K) HDC of 2,4-dichlorophenol. Two 1% w/w supported gold catalysts have been prepared by: (i) stepwise deposition of Au on α-Fe(2)O(3) with subsequent temperature-programmed reduction at 673 K (Au/Fe(3)O(4)-step); (ii) direct deposition of Au on Fe(3)O(4) (Au/Fe(3)O(4)-dir). TEM analysis has established the presence of Au at the nano-scale with a greater mean diameter (7.6 nm) on Au/Fe(3)O(4)-dir relative to Au/Fe(3)O(4)-step (4.5 nm). We account for this difference in terms of stronger (electrostatic) precursor/support interactions in the latter that can be associated with the lower pH point of zero charge (with respect to the final deposition pH) for Fe(2)O(3). Both catalysts promoted the preferential removal of the ortho-Cl substituent in 2,4-dichlorophenol, generating 4-chlorophenol and phenol as products of partial and total HDC, respectively, where Au/Fe(3)O(4)-step delivered a two-fold higher rate (2 × 10(-4) mol(Cl) h(-1) m(Au)(-2)) when compared with Au/Fe(3)O(4)-dir. This unprecedented selectivity response is attributed to activation of the ortho-C-Cl bond via interaction with electron-deficient Au nanoparticles. The results demonstrate the feasibility of a controlled recovery/recycling of chlorophenol waste using nano-structured Au catalysts.
催化加氢脱氯（HDC）是一种有效的解毒氯化废物的方法。已经在气相（1 大气压，423 K）中二氯苯酚的 HDC 中测试了负载在 Fe(3)O(4)上的金纳米粒子。通过以下两种方法制备了 2% w/w 的负载金催化剂：（i）在α-Fe(2)O(3)上逐步沉积 Au，随后在 673 K 下进行程序升温还原（Au/Fe(3)O(4)-step）；（ii）直接在 Fe(3)O(4)上沉积 Au（Au/Fe(3)O(4)-dir）。TEM 分析表明，Au/Fe(3)O(4)-dir 上的 Au 纳米颗粒具有较大的平均直径（7.6nm），而 Au/Fe(3)O(4)-step 上的 Au 纳米颗粒的平均直径为 4.5nm。我们认为这是由于后者中更强的（静电）前体/载体相互作用导致的，这可以与 Fe(2)O(3)相对于最终沉积 pH 的零电荷点（pHpzc）较低有关。两种催化剂都促进了 2,4-二氯苯酚中邻-Cl 取代基的优先去除，生成 4-氯苯酚和苯酚作为部分和完全 HDC 的产物，其中 Au/Fe(3)O(4)-step 的速率是 Au/Fe(3)O(4)-dir 的两倍（2×10(-4)mol(Cl) h(-1) m(Au)(-2)）。这种前所未有的选择性响应归因于通过与缺电子的 Au 纳米粒子相互作用激活邻-C-Cl 键。结果表明，使用纳米结构 Au 催化剂可以实现对氯苯酚废物的可控回收/再循环。
