Red mud-based catalysts for the catalytic removal of typical air pollutants: A review

Red mud, as a solid waste produced during the alumina production, can cause severe eco-environmental pollution and health risks to human. Therefore, the resourcing of this type of solid waste is an effective way for the sustainable development. This paper reviews the recent progress on red mud-based catalysts for the removal of typical air pollutants, such as the catalytic reduction of nitrogen oxides (NO_x) by NH₃ (NH₃-SCR) and the catalytic oxidation of CO and volatile organic compounds (VOCs). The factors influencing the catalytic performance and the structure-activity relationship have been discussed. Future prospects and directions for the development of such catalysts are also proposed. This review would benefit for the high value-added utilizations of red mud in mitigating atmospheric pollutions.

Catalytic ammonia reforming: alternative routes to net-zero-carbon hydrogen and fuel

Ammonia is an energy-dense liquid hydrogen carrier and fuel whose accessible dissociation chemistries offer promising alternatives to hydrogen electrolysis, compression and dispensing at scale. Catalytic ammonia reforming has thus emerged as an area of renewed focus within the ammonia and hydrogen energy research & development communities. However, a majority of studies emphasize the discovery of new catalytic materials and their evaluation under idealized laboratory conditions. This Perspective highlights recent advances in ammonia reforming catalysts and their demonstrations in realistic application scenarios. Key knowledge gaps and technical needs for real reformer devices are emphasized and presented alongside enabling catalyst and reaction engineering fundamentals to spur future investigations into catalytic ammonia reforming.

Insights into modified red mud for the selective catalytic reduction of NOx: Activation mechanism of targeted leaching

Red mud (RM) is a solid waste rich in iron oxide, which has the potential to be utilized as the catalyst for selective catalytic reduction (SCR) of NO_x. We pretreated the RM sample with the selective acid leaching method, after which 97.6 % of the alkali was neutralized, and only 8 % of the Fe₂O₃ were leached out. Once leached, the RM samples were activated for the SCR reaction. It showed NO_x conversions above 90 % in 310-430 °C and exhibited high resistance to SO₂ and H₂O. After leaching, i. the S_BET reached twice as before; ii. the sintering caused by alkali was eliminated; iii. the activated RM exhibited improved Fe³⁺/Fe²⁺ ratio and enhanced chemisorbed surface oxygen (O_α); iv. the oxygen mobility and the surface acidity were promoted. Overall, the selective acid leaching is an efficient method to activate RM for the SCR reaction. The RM based catalysts can be an alternative for SCR technology.

Noble Metal Nanoparticles Incorporated Siliceous TUD-1 Mesoporous Nano-Catalyst for Low-Temperature Oxidation of Carbon Monoxide

This report, for the first time, demonstrated the low-temperature oxidation of carbon monoxide (CO) using nano-catalysts consisting of noble metal nanoparticles incorporated in TUD-1 mesoporous silica nano-structures synthesized via a one-pot surfactant-free sol–gel synthesis methodology. Herein, we investigated a nano-catalyst, represented as M-TUD-1 (M = Rh, Pd, Pt and Au), which was prepared using a constant Si/M ratio of 100. The outcome of the analytical studies confirmed the formation of a nano-catalyst ranging from 5 to 10 nm wherein noble metal nanoparticles were distributed uniformly onto the mesopores of TUD-1. The catalytic performance of M-TUD-1 catalysts was examined in the environmentally impacted CO oxidation reaction to CO₂. The catalytic performance of Au-TUD-1 benchmarked other M-TUD-1 catalysts and a total conversion of CO was obtained at 303 K. The activity of the other nano-catalysts was obtained as Pt-TUD-1 > Pd-TUD-1 > Rh-TUD-1, with a total CO conversion at temperatures of 308, 328 and 348 K, respectively. The Au-TUD-1 exhibited a high stability and reusability as indicated by the observed high activity after ten continuous runs without any treatment. The outcomes of this research suggested that M-TUD-1 are promising nano-catalysts for the removal of the toxic CO gas and can also potentially be useful to protect the environment where a long-life time, cost-effectiveness and industrial scaling-up are the key approaches.

Mn-Doped material synthesized from red mud and rice husk ash as a highly active catalyst for the oxidation of carbon monoxide and p-xylene

Red muad and rice husk ash were treated without neutralization by acid to produce a support material (RR).

High-surface-area activated red mud for efficient removal of methylene blue from wastewater

Red mud was activated by a digestion–precipitation method, resulting in a mesostructure with high surface area, and the activated red mud was further used as the adsorbent for methylene blue removal. The physicochemical properties of the resultant samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry analysis, and nitrogen sorption techniques. Batch studies were measured to investigate the influence factors including adsorbent dosage, contact time, pH, and initial concentration. It was revealed that the activated red mud was highly efficient for removal of methylene blue. Adsorption experiments were found to be better achieved in faintly acidic and alkaline conditions, where the adsorption capacity of activated red mud and activated red mud-200 reached 232 and 274 mg/g at pH 7.0, respectively. Langmuir, Freundlich, Temkin isotherms, and pseudo-second-order kinetic model fitted the experimental data well, demonstrating an electrostatic interaction mechanism.

The recycle of red mud as excellent SCR catalyst for removal of NOx

The red mud is reused as catalyst with excellent DeNO_x efficiency at high temperature by milling and neutralization method.