Synthesis and catalytic evaluation of nickel supported on fibrous zeolite-y for co2 reforming of ch4 / Siti Nurqurratulainie Binti Miskan

Faculty of Chemical and Process Engineering Technology

Thesis (Master of Science) -- Universiti Malaysia Pahang – 2023

Includes bibliographical references

CO2 reforming CH4 (CRM) has been a promising approach to mitigate the CO2 and CH4 greenhouse gas emissions while evolving valuable syngas. The CRM reaction has been investigated extensively using a variety of supported metal catalysts, including Ni/zeolite-Y (Ni/HY). However, Ni/HY rapidly deactivated due to the carbon deposition and metal sintering, which arose from the weak metal-support interaction. Therefore, this study synthesizes and characterizes the modified fibrous zeolite-Y catalyst (FHY). Next, to examine the catalytic activity of synthesized FHY catalysts toward CRM. Ni/FHY catalysts were prepared by modifying HY into FHY using a microemulsion system coupled with the HY crystal-seed crystallization method, followed by the impregnation of Ni to the synthesized FHY and commercial HY. XRD, FTIR, BET, TEM, FESEM-EDX, CO2-TPD, and H2-TPR determined the properties of Ni/FHY. At the same time, CRM evaluation was conducted using a stainless steel fixed-bed reactor at a reaction temperature of 700 oC, gas hourly space velocity of 25,000 mL/g.h, and CH4/CO2 ratio of 1. The results showed that Ni/FHY (𝑋𝐶𝐻4=90.0%,𝑋𝐶𝑂2=85.9%,𝐻2/𝐶𝑂=0.85) possessed higher performance at a temperature of 700 oC compared to Ni/HY (𝑋𝐶𝐻4=85.9%,𝑋𝐶𝑂2=84.9%,𝐻2/𝐶𝑂=0.73) attributed to the fascinating characteristics of FHY that allowed a homogenous and better Ni distribution with a smaller Ni crystallite size, thus strengthening the metal-support interaction. The effect of Ni loadings (1, 3, 5, and 10 wt.%) showed that 5Ni/FHY had the best catalytic performance. The excellent performance of 5Ni/FHY because of the strong interaction between Si-O-Ni, the moderate size of the NiO crystallites (9.35 nm), and the even distribution of the active metals led to a strong synergistic effect between the Ni metal active sites and FHY. Moreover, the operating conditions of Ni/FHY over CRM were optimized using response surface methodology (RSM) under independent variables of reaction temperature (X1, 700-900 oC), gas hourly space velocity (X2, 15,000-35,000 mL/g.h), and CH4/CO2 ratio (X3, 1-3), with response variables of CH4 conversion (Y1), CO2 conversion (Y2), and H2/CO ratio (Y3). The optimal reaction conditions were found at X1 = 833 oC, X2 = 24,968 mL/g.h, and X3 = 2.08, with Y1 = 94.5%, Y2 = 88.3%, and Y3 = 1.02. This study also proved that the synthesized Ni/FHY catalyst was appreciably stable for 90 h time-on-stream with the performance of 𝑋𝐶𝐻4=93.5%,𝑋𝐶𝑂2=89.1% and could be regenerated by air. In summary, Ni/FHY was successfully synthesized and emerged as a high sustainability catalyst for efficient syngas production via CRM under optimal conditions generated from RSM. The 5Ni/FHY catalyst performed the best with high stability under optimum conditions generated by RSM and proved its ability to be regenerated by air.