用活性炭负载的钯基催化剂催化含硝酸根水外文翻译资料

 2022-01-30 10:01

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用活性炭负载的钯基催化剂催化含硝酸根水

Abstract The performance of carbon-supported, Pd bimetallic catalysts for nitrate reduction has been investigated. Pd–In and Pd–Sn catalysts have been tested for a range of nitrate concentration up to 1000 ppm in acidic and close to neutral pH. Pd–Cu was also studied at pH 5 for reference. Nitrate reduction was inhibited strongly by nitrite and moderately by sulphate. Activated carbon catalysts are shown to display an activity similar to metal oxide supported catalysts. copy; 2002 Elsevier Science B.V. All rights reserved.

研究碳负载的Pd双金属催化剂用于硝酸盐还原的性能。 已经测试Pd-In和Pd-Sn催化剂在酸性和接近中性pH下的一系列硝酸盐浓度高达1000ppm。 在pH 5下研究了Pd-Cu以供参考。 亚硝酸盐强烈抑制硝酸盐还原，硫酸盐适度抑制硝酸盐还原。 显示活性炭催化剂显示出与金属氧化物负载催化剂类似的活性。

1. Introduction

1.简介

Pollution of water with nitrate ions is a widespread problem arising from the development of agriculture and industrialisation. Conventional techniques such as ion exchange, reverse osmosis and electrodialysis allow effective removal of nitrates, but lead to the production of highly concentrated secondary waste stream. Catalytic reduction of nitrate to nitrogen is a promising process for removal of nitrate from water without the drawbacks of conventional methods [1–5]. Pd bimetallic catalysts, especially Pd–Cu, Pd–Sn, and Pd–In-supported on metal oxides, have proved to be the most effective for nitrate reduction according to the scheme in Fig. 1 [4]. Much effort has been devoted to developing a one-stage treatment process aimed at drinking water using a single catalyst. The reaction scheme of Fig. 1, however, lends itself to a two-stage process with nitrate reduction to nitrite in the first stage [6], and nitrite reduction in the second stage, which allows catalysts optimised for each stage. Such a process may be more appropriate for application to industrial effluent where there may be high concentration of nitrate, other competing ions, and low pH. Under more severe conditions, especially low pH, problems are likely to arise with the stability of the catalyst support. The present study reported here, has explored the utility of activated carbon as a support for Pd bimetallic catalysts for catalytic reduction of nitrate under low pH conditions. High nitrate concentrations and the influence of competing nitrite and sulphate ions are also investigated. Emphasis in this preliminary study has been placed on the activity and selectivity of Pd–In, Pd–Sn, and Pd–Cu for catalytic reduction of nitrate to nitrite, as may be appropriate to a first stage of a two-stage catalytic process.

硝酸根离子污染水是农业和工业化发展中普遍存在的问题。诸如离子交换，反渗透和电渗析的常规技术可以有效去除硝酸盐，但产生高度浓缩的二次废物流。将硝酸盐催化还原成氮气是一种很有前途的从水中除去硝酸盐的方法，没有传统方法的缺点。根据图1中的方案，Pd双金属催化剂，特别是Pd-Cu，Pd-Sn和Pd-In负载在金属氧化物上，已被证明是最有效的硝酸盐还原方法。投入了大量精力来开发单一催化剂的旨在饮用水的一步处理法。然而，图1的反应方案适用于两阶段过程，第一阶段硝酸盐还原为亚硝酸盐，第二阶段亚硝酸盐还原，这使得催化剂可以针对每个阶段进行优化。这种方法可能更适合应用于工业废水，其中可能存在高浓度的硝酸盐，其他竞争离子和低pH。在更苛刻的条件下，特别是低pH下，催化剂载体的稳定性可能会出现问题。本文报道的研究探讨了活性炭作为Pd双金属催化剂在低pH条件下催化还原硝酸盐的载体的用途。还研究了高硝酸盐浓度以及亚硝酸盐和硫酸根离子的影响。该初步研究的重点放在Pd-In，Pd-Sn和Pd-Cu的活性和选择性上，用于将硝酸盐催化还原成亚硝酸盐，这可能适合于两阶段催化过程的第一阶段。

2. Experimental

2.1. Catalyst preparation

2.实验

2.1催化剂制备

A commercially available 5 wt.% Pd on activated carbon catalyst (Aldrich), surface area of 800 m2 gminus;1, was used as base for the preparation of the bimetallic catalysts. Prior to impregnation the Pd base catalyst was ground to a particle size distribution with 99% of the particles below 13m. The metals associated to palladium (Me) were added to the base catalyst by the pore-filling method to give a nominal ratio Pd:Me of 4:1 by weight, similar to the preparation of Pd bimetallic catalysts on metal oxides supports [7–10]. Aqueous solutions of indium(III) nitrate pentahydrate, 99.999%; tin(II) chloride, 99.99 % and copper(II) chloride, 99.999% (all from Aldrich) were used. Metal chlorides have been reported as the “preferred precursors” [11]. XPS analysis of the present Pd–Sn and Pd–Cu catalysts showed that no chloride remains from the impregnation after calcination and reduction. The amount of water required for the pore filling method was determined by weighing. The impregnated catalysts were dried in a ventilated oven at 373 K until complete dryness. The Pd–Cu catalyst was calcined in a nitrogen flow at 773 K for 3 h, Pd–In and Pd–Sn catalysts were calcined in an air flow at 393 K for 3 h (heating rate 1 K minminus;1 in all cases). Calcination temperatures were determined from a TPO study of the catalysts.

使用市售的5重量％Pd /活性炭催化剂，表面积为800m2 g-1，作为制备双金属催化剂原料。在浸渍之前，将Pd催化剂研磨成粒度分布，其中99％的颗粒低于13mu;m。通过孔填充法将与钯和相关的金属加入到催化剂中，得到标称比率Pd：Me为4：1（重量），类似于在金属氧化物载体上制备Pd双金属催化剂。硝酸铟（III）五水合物的水溶液，99.999％;使用氯化锡（II），99.99 ％和氯化铜（II），99.999％（均来自Aldrich）。据报道，金属氯化物是“优选的前体”。本发明Pd-Sn和Pd-Cu催化剂的XPS分析表明，在煅烧和还原后，浸渍中没有氯化物残留。通过称重确定孔填充方法所需的水量。将浸渍的催化剂在通风烘箱中在373K下干燥直至完全干燥。将Pd-Cu催化剂在氮气流中在773K下煅烧3小时，Pd-In和Pd-Sn催化剂在空气流中在393K下煅烧3小时（在所有情况下加热速率1K min -1） 。煅烧温度由催化剂的TPO研究确定。

XRD of Pd–In and Pd–Sn do not display intense peaks of either Pd or the added co-metal, which is taken to be indicative of a good dispersion of the active metals on the support [7,11]. XPS analysis (VG ESCALAB MkII) supports this conclusion.

Pd-In和Pd-Sn的XRD不显示Pd或添加的共金属的强峰，这被认为表明活性金属在载体上的良好分散[7,11]。 XPS分析（VG ESCALAB MkII）支持这一结论。

2.2. Catalytic tests

2.2催化试验

Catalytic tests were conducted in a semi-batch mode in a purpose-built stirred baffled glass reactor (liquid volume = 1 l) at 298 K under atmospheric pressure using a gas flow of 400 ml minminus;1 of 50% hydrogen/nitrogen. Distilled and deionised water was used with nitrate ions introduced as potassium nitrate. Prior to the experiment the water was degassed with a flow of 200 ml minminus;1 of nitrogen. Reduction was carried out in a dedicated reactor attached to the main reactor for 1/2 h at reduction temperatures obtained from a TPR study. The reduction temperatures used were 373 K for Pd–In and Pd–Sn catalysts, and 423 K for the Pd–Cu catalyst. The reduced catalyst was transferred into the nitra

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