Modified Zeolite Catalyst for a NOx Selective Catalytic Reduction Process in Nitric Acid Plants

Abstract

Natural zeolite of the heulandite-type framework was modified with iron and tested as a catalyst for the selective catalytic reduction of nitrogen oxides with ammonia (NH3-SCR) in the temperature range of 150–450 °C. The catalyst was prepared at a laboratory scale in a powder form and then the series of experiments of its shaping into tablets was conducted. Physicochemical studies of the catalyst (N2 sorption at −196 °C, FT-IR, XRD, UV-vis) were performed to determine the textural and structural properties and identify the surface functional groups, the crystalline structure of the catalysts and the form and aggregation of the active phase. The activity tests over the shaped catalyst were performed industry-reflecting conditions, using tail gases from the pilot nitric acid plant. The influence of a temperature, catalyst load, and the amount of reducing agent (ammonia) on the NOx reduction process were investigated. The results of catalytic tests that were performed on model gas mixture showed that non-modified clinoptilolite exhibited around 58% conversion of NO at 450 °C. The temperature window of the shaped catalyst shifted to a higher temperature range in comparison to the powder sample. The catalytic performance of the shaped Fe-clinoptilolite in the industry-reflecting conditions was satisfactory, especially at 450 °C. Additionally, it was observed that the ratio of N2O concentration downstream and upstream of the catalytic bed was below 1, which indicated that the catalyst exhibited activity in both DeNOx and DeN2O process.

Physicochemical Features and NH3-SCR Catalytic Performance of Natural Zeolite Modified with Iron—The Effect of Fe Loading

“…The reflection at 2θ of 26.6 • corresponds to SiO 2 , while those at 21.9 and 28.1 • are due to the presence of cristobalite impurities in the solid [13]. The observed diffraction maxima are in good agreement with those reported in the literature [18,22]. The comparative analysis of the materials showed that protonation by acid treatment did not result in any noticeable structural changes.…”

“…Highly satisfactory activity of iron-modified clinoptilolite in SCR with ammonia was confirmed in the previous study [18]. It was found that raw clinoptilolite in a form of fine grain showed 30% of NO conversion in the range of 350-450 • C. The high efficiency of the material in NH 3 -SCR with the gas mixture reflecting the industrial composition was also confirmed.…”

“…Another study conducted by the authors [15,17] concerned clinoptilolite as a possible support for the catalyst of SCR with propane. However, only few studies have explored zeolite as a support for SCR with ammonia [13,18].…”

Low-Temperature Selective Catalytic Reduction DeNOX and Regeneration of Mn–Cu Catalyst Supported by Activated Coke

“…More importantly, the optimum temperature ranges for the use of the vanadium–tungsten–titanium catalysts are 300~400 °C, which does not match with the low-temperature selective catalytic reduction process. In recent years, many scholars have attempted to develop efficient, cheap and low-temperature SCR catalysts [ 5 , 6 , 7 , 8 , 9 ]; in particular, the activated carbon attracted extensive attention. As a carbon-based porous medium, activated coke has similar structural characteristics to the activated carbon, and its chemical stability is basically the same as the activated carbon.…”

Оптическая И Эпр-Спектроскопия Модифицированного Микроволновым Методом Натурального Цеолита

“…ниже). В работе [14] при изучении натурального цеолита (клиноптилолита) и модифицированного железом в спектрах поглощения первую полосу связывают с переносом заряда кислорода на катионы Fe 3+ в октаэдрической координации, а вторую -с наличием внекаркасных олигомеров FeO x .…”