Mechanical Strength Of Catalyst Research Articles

Nickel catalysts for nitrogen–hydrogen mixture purification from carbon oxides

Objectives.This study is devoted to developing new-generation nickel (Ni) catalysts for the purification of a nitrogen–hydrogen mixture from carbon oxides, which should encompass the best qualities of the NIAP-07-series solid catalysts.Methods. This study used derivatographic and radiographic methods; temperature-programmed recovery, decomposition, and joint temperature-programmed decomposition and recovery; and low-temperature nitrogen adsorption (specific surface determination). The mechanical strength of catalysts was determined using an MP-2C device by crushing granules with an applied load on the end face. The chemical composition and catalytic activity were determined by the methods of TU 2178-003-00209510 Technical Conditions.Results.Many studies regarding Ni–aluminum (Al)–calcium (Ca) methanation catalyst at all stages of its preparation have been conducted. It is demonstrated that Ni hydrocarboxyaluminate, a precursor of the active component of the catalyst, is formed when Ni hydroxocarbonate is mixed with active alumina in the presence of an aqueous solution of ammonia, and its chemical formula is established. Moreover, it was found that the mechanical strength of the catalyst is determined by the amount of industrial Ca aluminate added to the Ni–Al composition. The compositions of catalysts with different contents of the active component have been optimized.Conclusions.The developed catalyst has a low activation temperature and high catalytic activity, thermal stability, and mechanical strength and is resistant to organic and alkaline carbon dioxide absorbers. The catalyst can be produced in the form of a ring, cylindrical tablets, and extrudates of various geometric sizes. The methanation unit at Stavrolen (Budennovsk, Stavropol krai, Russia) has begun commercially operating the catalyst.

SO2 promoted alkali metal doped Ag/Al2O3 catalysts for CH4-SCR of NOx

A study of the lean NOx reduction activity in the presence of SO2 and water over alkali promoted Ag/Al2O3 catalysts has been done using methane as a reductant. The alkali doped materials are synthesized by the co-impregnation method. Their promotional behavior, existence of several silver species and improved adsorption properties have been thoroughly investigated by various techniques: XRD, XANES, TEM, UV–Vis DRS, SO2 TPD and NO TPD. The evaluated samples exhibited high surface area around 220m2g−1. TEM results demonstrated the presence of highly dispersed nano sized silver particles on surface, where the addition of alkali metals slightly enhanced the crystallization of silver. Moreover, standard XRD profiles of fresh and used samples indicate the high durability and mechanical strength of catalysts. These findings are in line with the time-on-stream studies. The XANES results revealed that the edge spectra of prepared materials are similar to that of the reference Ag2SO4. From XANES and UV–Vis DRS, the presence of crystalline Ag0 and Ag+ species were identified. Poor activity of Na promoted sample is attributed to absence of suitable amount of ionic silver compounds. However, the synthesized alkali doped materials showed the promotional deNOx conversions in the presence of SO2 and H2O stream. Among the investigated samples K–Ag/Al2O3 and Cs–Ag/Al2O3 exhibited higher NOx conversions and thermal stability. The higher SCR of NOx was explained by the NO adsorption properties identified from the NO TPD studies.

Effect of abnormal treatment on the mechanical strength of iron-based high-temperature shift catalyst

The abnormal conditions encountered by an iron-based high-temperature water-gas shift catalyst in different processing stages and the effect of these conditions on the mechanical strength of the catalyst have been investigated by experimental simulation and Weibull statistics. In the process of production, heating and reduction, the catalyst can often be over-heated. Over-heating or thermal treating of the powder before pelleting as well as the pellets, and thermal shock in the reduction lower the mean horizontal crushing strength and the Weibull modulus, and increase the probability of strength failure by 3 to 10 orders. Absorption of moisture and wetness by water of the pellets, and steam or water shock in the reduction increase this probability by several orders. The mechanical treatment by dropping down the pellets on the floor also lowers the strength. The results in this paper show that properly pelleted and reduced samples possess a very high and reliable strength, for instance, the best reduced sample has a Weibull modulus up to 12.8. The probability of failure of this sample at 10 kg/ pellet is as low as 4.16·10 −11. These results show the potentiality in increasing catalyst mechanical strength, and show that due to their brittleness, the catalysts should be properly processed.