活性炭负载Pd催化剂常温直接合成过氧化氢

Direct Synthesis of H_(2)O_(2) from H_(2) and O_(2) on Activated Carbon Supported Pd Catalysts at Ambient Temperature

选用4种不同的活性炭作载体,使用化学吸附法制备Pd/AC催化剂,并测定催化剂对氢气氧气直接合成过氧化氢的活性.为探究活性炭物理化学性质对催化活性的影响,使用TEM、XPS、XRD、Boehm滴定、N_(2)吸附脱附等手段对Pd/AC催化剂和活性炭载体进行系统的表征测试,结果表明:Pd的吸附状态几乎不受活性炭的物理化学性质的影响;选择比表面积较大、石墨化程度较高、表面酸性较强且N含量较低的活性炭作载体,有利于获得活性较高的催化剂.活性炭的NH_(3)改性实验结果表明:由于吡啶型N和Pd之间的强配位能力,导致吸附的Pd物种不能在反应过程中被还原,因而吡啶型N含量较高的催化剂活性较低,甚至没有催化活性.

In this paper,the reaction of direct synthesis of H_(2)O_(2)from H_(2)and O_(2)was conducted on Pd/AC catalysts.Four different kinds of activated carbons were selected as the supports,and the supported Pd/AC catalysts were prepared by the chemical adsorption method.For a better understanding of the influence of the physicochemical properties of activated carbons on the catalytic performance of Pd/AC,these Pd/AC catalysts and activated carbons were systemically characterized by TEM,XPS,XRD,Boehm titration,and in addition to N_(2) adsorption and desorption.The characterization results suggested that the physicochemical properties of activated carbons almost had no effect on the status of adsorption of Pd species.The characterization results also revealed that the activated carbon with higher specific surface area and graphitization degree,larger content of acid functional groups and lower content of N-containing groups was preferred for catalyst preparation.The results of the NH_(3)modification experiments indicated that the adsorbed Pd species can’t reduce to Pd^(0) in the direct synthesis reaction,because of the strong coordination capacity between Pd and pyridinic N.This was exactly the reason why the increasing of the pyridinic N in activated carbon always led to a poor catalytic performance,and in some extreme cases the Pd catalysts were totally poisoned by pyridinic N.