Partial hydrogenation of 1,3-butadiene over nickel with alumina and niobium supported catalysts

The hydrogenation of 1,3 butadiene (BD) is an important industrial process that is generally used to generate butenes and aromatics, which are important petrochemicals and constituents of transportation fuels. Ni-based catalysts have gained increasing interest in the academic community and industry because of their superior hydrogenation activity, ability to exist in multiple oxidation states and most importantly, affordability compared to the less-abundant precious metal catalysts. In this work, we explore the ability of alumina (Al2O3) and niobia (Nb2O5) as catalytic supports for Ni as the active metal since they have shown excellent potential for hydrogenation of alkenes. Specifically, we compare the metal-support interactions, which disperse Ni effectively throughout the catalyst surface, textural and pore parameters, Ni crystallite size, surface morphology, elemental composition, coke formation and tendencies of both catalysts through extensive characterization techniques such as H2-temperature programmed reduction (H2-TPR), N2-adsorption-desorption, X-ray diffraction (XRD), scanning electron microscopy combined with electron-dispersive spectra (SEM-EDS), and thermal analysis of the spent catalysts. Limited reports on the use of niobium oxides and alumina as supports for Ni in the partial hydrogenation of BD prompted us to explore this literature gap. The catalytic reactions were conducted using a quartz tube reactor between a temperature range of 50 and 400 °C at regular intervals of 50 °C under operating pressures of 1 atm. A comprehensive analysis of the products from the reaction was carried out using gas-chromatography with mass spectrometry (GC-MS) detector and corroborated these results with those from infrared spectroscopy (FTIR). Reaction mechanisms of aliphatic and aromatic product formation were proposed and verified with literature and our own characterization results. The tests on the spent catalysts also helped to reveal the extent of deactivation of the catalysts due to carbon deposition. Mechanisms of catalyst deactivation and nature of carbonaceous deposits were explored and elaborate scientific reasoning was provided as to why Ni/alumina showed better performance in terms of product yields and BD conversion. Ways to mitigate the harmful effects of coke formation and its deposition are also discussed. The novelty of our work is that a comprehensive comparison of the performance of Ni/alumina and Ni/niobia for hydrogenation of BD along with extensive discussions on coke formation, its chemical nature and proposed reaction chemistry based on obtained characterization results of the catalysts and the products of BD hydrogenation has not been done before for this system. In this way, we show the low-temperature conversion of BD represents an economically efficient and relatively simple method to convert toxic, carcinogenic and environmentally hazardous BD into high-value products using low-cost and chemically efficient catalysts.