CeO(2)-TiO(2) (CeTi) catalysts synthesized by an ultrasound-assisted impregnation method were employed to oxidize elemental mercury (Hg(0)) in simulated low-rank (sub-bituminous and lignite) coal combustion flue gas. The CeTi catalysts with a CeO(2)/TiO(2) weight ratio of 1-2 exhibited high Hg(0) oxidation activity from 150 to 250 °C. The high concentrations of surface cerium and oxygen were responsible for their superior performance. Hg(0) oxidation over CeTi catalysts was proposed to follow the Langmuir-Hinshelwood mechanism whereby reactive species from adsorbed flue gas components react with adjacently adsorbed Hg(0). In the presence of O(2), a promotional effect of HCl, NO, and SO(2) on Hg(0) oxidation was observed. Without O(2), HCl and NO still promoted Hg(0) oxidation due to the surface oxygen, while SO(2) inhibited Hg(0) adsorption and subsequent oxidation. Water vapor also inhibited Hg(0) oxidation. HCl was the most effective flue gas component responsible for Hg(0) oxidation. However, the combination of SO(2) and NO without HCl also resulted in high Hg(0) oxidation efficiency. This superior oxidation capability is advantageous to Hg(0) oxidation in low-rank coal combustion flue gas with low HCl concentration.

CeO2-TiO2 catalysts for catalytic oxidation of elemental mercury in low-rank coal combustion flue gas.

Promotional mechanisms of activity and SO2 tolerance of Co- or Ni-doped MnOx-CeO2 catalysts for SCR of NOx with NH3 at low temperature

TiO 2 supported Mn-Ce mixed oxides (Mn-Ce/Ti) synthesized by an ultrasound-assisted impregnation method were employed to oxidize elemental mercury (Hg 0 ) at low temperatures in simulated low-rank (sub-bituminous and lignite) coal combustion flue gas and corresponding selective catalytic reduction (SCR) flue gas. The catalysts were characterized by BET surface area analysis, X-ray diffraction (XRD) measurement and X-ray photoelectron spectroscopy (XPS) analysis. The combination of MnO x and CeO 2 resulted in significant synergy for Hg 0 oxidation. The Mn-Ce/Ti catalyst was highly active for Hg 0 oxidation at low temperatures (150–250 °C) under both simulated flue gas and SCR flue gas. The dominance of Mn 4+ and the presence of Ce 3+ on the Mn-Ce/Ti catalyst were responsible for its excellent catalytic performance. Hg 0 oxidation on the Mn-Ce/Ti catalyst likely followed the Langmuir–Hinshelwood mechanism, where reactive species on catalyst surface react with adjacently adsorbed Hg 0 to form Hg 2+ . NH 3 consumed the surface oxygen and limited the adsorption of Hg 0 , hence inhibiting Hg 0 oxidation over Mn-Ce/Ti catalyst. However, once NH 3 was cut off, the inhibited mercury oxidation activity could be completely recovered in the presence of O 2 . This study revealed the possibility of simultaneously oxidizing Hg 0 and reducing NO x at low flue gas temperatures. Such knowledge is of fundamental importance in developing effective and economical mercury and NO x control technologies for coal-fired power plants.

Superior activity of MnOx-CeO2/TiO2 catalyst for catalytic oxidation of elemental mercury at low flue gas temperatures

Manganese oxide has been recognized as one of the most promising gaseous heterogeneous catalysts due to its low cost, environmental friendliness, and high catalytic oxidation performance. Mn-based oxides can be classified into four types: (1) single manganese oxide (MnOx), (2) supported manganese oxide (MnOx/support), (3) composite manganese oxides (MnOx-X), and (4) special crystalline manganese oxides (S-MnOx). These Mn-based oxides have been widely used as catalysts for the elimination of gaseous pollutants. This review aims to describe the environmental applications of these manganese oxides and provide perspectives. It gives detailed descriptions of environmental applications of the selective catalytic reduction of NOx with NH3, the catalytic combustion of volatile organic compounds, Hg0 oxidation and adsorption, and soot oxidation, in addition to some other environmental applications. Furthermore, this review mainly focuses on the effects of structure, morphology, and modified elements and on the rol...

Gaseous Heterogeneous Catalytic Reactions over Mn-Based Oxides for Environmental Applications: A Critical Review.

Nowadays, an increasing attention has been paid to the technologies for removing mercury from flue gases. Up to date, no optimal technology that can be broadly applied exists, but the heterogeneous catalytic oxidation of mercury is considered as a promising approach. Based on a brief introduction of the pros and cons of traditional existing technologies, a critical review on the recent advances in heterogeneous catalytic oxidation of elemental mercury is provided. In this contribution, four types of Hg oxidation catalysts including noble metals, selective catalytic reduction (SCR) catalysts, transition metals, and fly ash have been summarized. Both the advantages and disadvantages of these catalysts are described in detail. The influence of various acidic gases including SO2, SO3, NH3, NOx, HCl, Cl2, etc. have been discussed as well. We expect this work will shed light on the development of heterogeneous catalytic oxidation of elemental mercury technology in flue gases, particularly the synthesis of novel...

A Critical Review on the Heterogeneous Catalytic Oxidation of Elemental Mercury in Flue Gases

In order to facilitate the removal of elemental mercury (Hg0) from coal-fired flue gas, catalytic oxidation of Hg0 with manganese oxides supported on inert alumina (α-Al2O3) was investigated at lower temperatures (373−473 K). To improve the catalytic activity and the sulfur-tolerance of the catalysts at lower temperatures, several metal elements were employed as dopants to modify the catalyst of Mn/α-Al2O3. The best performance among the tested elements was achieved with molybdenum (Mo) as the dopant in the catalysts. It can work even better than the noble metal catalyst Pd/α-Al2O3. Additionally, the Mo doped catalyst displayed excellent sulfur-tolerance performance at lower temperatures, and the catalytic oxidation efficiency for Mo(0.03)−Mn/α-Al2O3 was over 95% in the presence of 500 ppm SO2 versus only about 48% for the unmodified catalyst. The apparent catalytic reaction rate constant increased by approximately 5.5 times at 423 K. In addition, the possible mechanisms involved in Hg0 oxidation and the ...

Catalytic Oxidation of Elemental Mercury over the Modified Catalyst Mn/α-Al2O3 at Lower Temperatures

MnOx/Al2O3 catalysts (i.e., impregnating manganese oxide on alumina) were employed to remove elemental mercury (Hg0) from flue gas. MnOx/Al2O3 was found to have significant adsorption performance o...

Adsorption and Catalytic Oxidation of Gaseous Elemental Mercury in Flue Gas over MnOx/Alumina

The performance of iodine on the removal of elemental mercury from the simulated coal-fired flue gas.

The removal characteristics of hydrogen sulfide were studied experimentally in the biofilters with fibrous peat and resin as the packed materials. The factors that influenced the removal efficiency of hydrogen sulfide were investigated. The biofilter with 100% of the peat showed higher removal capacity than the resin biofolter, but the gas flow resistance was lower in the latter. The mixture of the peat and resin as the packed material of the biofilter was proved to be an advisable method to keep the high removal capacity and reduce the gas flow resistance for a long-term operation. The flow resistance can decrease by 50% when 50% of the resin mixed with the peat, but the removal capacity was still considerable high. In addition, the removal kinetics in the biofilters were discussed, and the main kinetics parameters were determined experimentally. The maximum removal rate of hydrogen sulfide, Vmax , was about 620, 210 and 480 g/m3h in the biofilters with 100% peat, 100% resin and 50% peat mixture, respectively. The result was helpful to the design and optimization of the biofilter.

Removal Characteristics of Hydrogen Sulfide in Biofilters with Fibrous Peat and Resin

Elemental mercury in coal-fired flue gas is difficult to be removed efficiently by traditional Air Pollution Control Devices (APCD). It has been proved to a promising approach to convert elemental mercury to oxidized mercury, which is soluble and ready to be captured. The oxidants for the direct oxidation of elemental mercury by gas phase reaction were studied, and gaseous iodine was investigated in this paper. The reaction kinetics between elemental mercury and oxidants were determined experimentally. Iodine showed high performance to the oxidation of elemental mercury among these oxidants, and the 2nd rate constant was about 1.95times10-16cm3-molecules-1ldrs-1 at around 297 K. In addition, sulfur dioxide had very slight impact on the reaction kinetics between elemental mercury and iodine. However, nitric oxide showed a significant inhibition effect on this reaction.

Shaohua Qiao

Papers

Catalytic Oxidation of Elemental Mercury over the Modified Catalyst Mn/α-Al2O3 at Lower Temperatures

Adsorption and Catalytic Oxidation of Gaseous Elemental Mercury in Flue Gas over MnOx/Alumina

The performance of iodine on the removal of elemental mercury from the simulated coal-fired flue gas.

Removal Characteristics of Hydrogen Sulfide in Biofilters with Fibrous Peat and Resin

Preliminary Study on Oxidation of Elemental Mercury in the Presence of Gaseous Oxidants