The present disclosure provides SCR catalyst compositions capable of reducing nitrogen oxide (NO.sub.x) emissions in engine exhaust. The catalyst compositions include a reducible metal oxide support containing ceria, one or more transition metal oxides as a redox promotor; and an oxide of niobium, tungsten, silicon, molybdenum, or a combination thereof as an acidic promotor. The redox promotor and the acid promotor are both supported on the reducible metal oxide support. Further provided are SCR catalyst articles coated with such compositions, processes for preparing such catalyst compositions and articles, an exhaust gas treatment system including such catalyst articles, and methods for reducing NO.sub.x in an exhaust gas stream using such catalyst articles and systems.

Complexes of polyoxometalate (POM) cluster anions and nanoparticle (NP) cores, are disclosed, featuring inherent thermodynamic stability at least due to covalent bonds, which attach the POMs to the NP cores. The nanoparticles comprise a plurality of crystalline, polycrystalline or amorphous metal-oxide, metal oxyhydroxide and/or metal hydroxide compounds. The POM and NP, each independently, may comprise one, two, three or more different metal cations, particularly transition or main group metal cations. These complexes are highly soluble in water and inherently stable to oxidation and hydrolysis in a broad pH range. As such, the complexes are useful, inert alia, as improved soluble water-oxidation catalysts and stabilizers of metastable crystals.

There is disclosed a highly efficient and economical catalyst for carbon monoxide (CO) oxidation at low temperatures, using a non-noble transition metal composition of copper oxide (CuO), cerium oxide (CeO.sub.2), and niobium oxide (Nb.sub.2O.sub.5). The catalyst, designated as 10CuCeNb, is synthesized via the wet impregnation method and is composed of with 10% CuOCeO.sub.2 supported on Nb.sub.2O.sub.5. It shows a significantly improved performance with full CO conversion achieved at relatively low temperature of 150 C. It demonstrates high stability over a 12-hour reaction time. The activation energy (Ea) is 23.1 kJ mol.sup.1, supporting low-temperature CO oxidation with minimal energy input. The catalyst's high activity and stability are attributed to the formation of oxygen vacancies and active Lewis acid sites generated from the synergistic interaction between CuO, CeO.sub.2, and Nb.sub.2O.sub.5. This catalyst offers a cost-effective alternative to noble metal catalysts for use in catalytic converters, effectively reducing CO emissions in industrial and environmental applications.

A hydrogen production method includes the heating of a catalyst in a furnace under reducing conditions to a first temperature, exposing the catalyst to water at a second temperature, and forming oxygen and hydrogen by thermolysis of the water, where the catalyst may include a barium niobate-based perovskite structure having the chemical formula of Ba.sub.1x(AE).sub.xNb.sub.1(y+z)(AE).sub.yM.sub.zO.sub.3 wherein AE is an alkaline earth (AE) element and M is a metal. M may include a transition metal or a rare earth metal. AE may include Mg, Ca, Sr, or a combination thereof. AE may alternatively include K, Rb, Cs or a combination thereof. M may include Fe, Co, Ni, Y, Yb, W, Ta, Pr, or a combination thereof. M may include Sc, Ti, V, Cr, Mn, Cu, Zn, Zr, Mo, La, Ce, Sm, Gd, W or a combination thereof.