活性炭硝酸表面改性对催化剂分散度的影响

无论是活性炭作为催化剂载体还是在活性炭本身的催化制备过程中,催化剂在活性炭或活性炭前体上的高度分散都是至关重要的。通过X射线能谱(EDX)和扫描电子显微镜(SEM)技术直接观察、研究了活性炭表面经硝酸氧化改性对硝酸铜在煤基活性炭中分散度的影响。此外,将经硝酸表面改性的商品活性炭采用浸渍法负载上硝酸铜催化剂,再经水蒸气二次活化制备了一种新的活性炭。结果表明,硝酸处理造成活性炭吸附性能的下降,并且硝酸处理的强度越高,活性炭吸附性能的下降程度越大。然而,对硝酸处理的活性炭经简单的水洗可恢复其吸附性能。研究结果还表明,活性炭经硝酸氧化提高了炭表面含氧官能团的数量,使催化剂在活性炭的内外表面均能均匀分布,提高了催化剂的分散度和抗烧结能力。活性炭经硝酸改性后再负载硝酸铜进行二次活化制备高性能活性炭,可使硝酸铜的催化性能得到进一步的提升。

Influence of surface modification by nitric acid on the dispersion of copper nitrate in activated carbon

High degree dispersion of catalyst in activated carbon plays an essential role in the cases of either activated carbon being a catalyst carrier or the catalytic preparation of activated carbon itself. The effect of surface modification by HNO3 on the dispersion of Cu(NO3)2 in coal-based activated carbon was investigated by Energy Diffraction X-ray (EDX) and Scanning Electron Microscopy (SEM) techniques. Besides, activated carbons were prepared by re-activation of a commercial activated carbon loaded with Cu(NO3)2 after HNO3 modification. Results showed that treatment by HNO3 results in the rapid fall of adsorption capacity of the resulting activated carbon, and the greater the intensity of treatment, the more the decrease of adsorption capacity. However, washing of HNO3-treated activated carbon has the effect of restoring the adsorption capacity of activated carbon. Apart from this, oxidation of activated carbon by nitric acid leads to the increase of oxygen functional groups on carbon surface, results in the uniform distribution of catalyst (copper nitrate) on both the interior and exterior surfaces of the activated carbon, produces an enhancement of catalyst dispersion, and improves the anti-sintering ability of the catalyst particulates. As a result, the catalytic ability of copper nitrate on the carbon-steam reaction is enhanced when activated carbon modified by HNO3 is used as a precursor for the preparation of advanced activated carbon by a second activation.