Preparation Of Biomineralized MnO_x And Research On Low-temperature SCR Performance

Mn-based catalysts have become a research focus for low-temperature NH₃-SCR denitration catalysts due to their abundant valence states and strong low-temperature redox ability.Based on the environmental harmlessness,a biomineralized MnO_x catalytic material（MnO_x-LB）with excellent low-temperature catalytic reduction of NOx was constructed and developed.In this paper,the physicochemical properties of the MnO_x-LB catalyst and its surface NH₃-SCR reaction pathway were deeply analyzed through a series of characterizations.By changing the proportion of precursor solution,biological species and dosage,whether it was cultured with glucose,and roasting at high temperature,the influence of the precursor on the SCR performance of Mn-based-biomineralized material（MnO_x-LB）was investigated.Infrared spectroscopic analysis proved that the biological bacteria were successfully combined with MnO_x.The study found that the molar ratio of KMn O₄ to Mn SO₄·H₂O in the precursor solution was 6:1,and the catalyst prepared by lactic acid bacteria as the raw material of biological bacteria（100 m L dosage was 3 g）had better effect,and realized the NOx conversion rate under the experimental conditions.It was maintained at about 100%in the range of 100℃～200℃;the NOx conversion rate of the MnO_x-LB catalyst cultured with glucose decreased to a certain extent;the selectivity of the catalyst after burning at 300℃was slightly poor.In addition to the superior catalytic activity,the N₂ selectivity during the SCR reaction on the MnO_x-LB surface is significantly better than that of the conventional MnO_x.It is found that both belong to theδ-Mn O₂ crystal form,and the morphology is spherical composed of staggered curved nanosheets.Due to the synergistic effect between biomass and manganese species,MnO_x-LB forms Mn-O-C,Mn-C-N special structures,and the lattice distortion generates more oxygen vacancies to maintain charge neutrality.The superior N₂ selectivity of MnO_x-LB can be attributed to the fast NOx specific reaction rate,abundant oxygen vacancies and high Mn³⁺/Mn atomic ratio.The SCR reaction pathway of MnO_x-LB at low temperature（<200°C）mainly depends on the adsorbed NH₃ and NO₂ on the catalyst,following the Langmuir-Hinshelwood（L-H）mechanism.The N₂ selectivity of MnO_x-LB catalyst decreased with the increase of temperature,and a metal-doped biomineralized catalytic material（M-MnO_x-LB）was further constructed to achieve excellent activity and high N₂ selectivity at low temperature.The sequence of SCR activity of M-MnO_x-LB doped with different metal elements is Cr>Fe>Co>Cu>Zn,and the order of N₂ selectivity improvement is Cr>Co>Zn>Fe>Cu>>None（not doping）.The study found that the addition of metal elements did not change the crystal structure of MnO_x-LB,inhibited the formation of MnO_x phase to a certain extent,and formed a C-O-M structure,and the metal doping was beneficial to the electron transfer of the catalyst(Mⁿ⁺+Mn³⁺?M^m++Mn⁴⁺).In particular,the doping of Cr increases the active oxygen concentration on the surface of the Cr-MnO_x-LB catalyst and the effective synergy between Cr and Mn ions(Cr⁵⁺+2Mn³⁺?Cr³⁺+2Mn⁴⁺),which exhibits excellent SCR performance and high N₂selectivity.The coordinating NH₃ adsorbed on the Lewis acid sites on the surface and the NH₄⁺species adsorbed on the Br?nsted acidic sites are more abundant,providing more reactive species for the SCR reaction,following the L-H mechanism.