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In the last decades, environmental crises and increasing energy demand have motivated researchers to investigate the practical techniques for the production of clean fuels through renewable energy resources. It is essential to develop technologies to utilize glycerol as a byproduct derived from biodiesel. Glycerol is known as a sustainable and clean source of energy, which can be an alternative resource for the production of value-added chemicals and hydrogen. The hydrogen production via steam reforming (SR) of glycerol using Ni-based catalysts is one of the promising approaches for the entry of the hydrogen economy. The purpose of this review paper is to highlight the recent trends in hydrogen production over Ni-based catalysts using the SR of glycerol. The intrinsic ability of Ni to disperse easily over variable supports makes it a more viable active phase for the SR catalysts. The optimal reaction conditions have been indicated as 650–900 °C, 1 bar, and 15 wt% Ni in catalysts for high glycerol conversion. In this review paper, the effects of various supports, different promoters (K, Ca, Sr, Ce, La, Cr, Fe), and process conditions on the catalytic performance have been summarized and discussed to provide a better comparison for the future works. It was found that Ce, Mg, and La have a significant effect on catalytic performance as promoters. Moreover, SR of glycerol over hydrotalcite and perovskite-based catalysts have been reviewed as they suggest high catalytic performance in SR of glycerol with improved thermal stability and coke resistance. More specifically, the Ni/LaNi0.9Cu0.1O3 synthesized using perovskite-type supports has shown high glycerol conversion and sufficient hydrogen selectivity at low temperatures. On the other hand, hydrotalcite-like catalysts have shown higher catalytic stability due to high thermal stability and low coke formation. It is vital to notice that the primary concern is developing a high-performance catalyst to utilize crude glycerol efficiently.

Dimethyl ether (DME) is a synthetically produced alternative fuel to diesel-based fuel and could be used in ignition diesel engines due to increasing energy demand. DME is considered extremely clean transportation and green fuel because it has a high cetane number (around 60), low boiling point (−25 °C), and high oxygen amount (35 wt%) which allow fast evaporation and higher combustion quality (smoke-free operation and 90% fewer NOx emissions) than other alternative CO2-based fuels. DME can be synthesized from various routes such as coal, petroleum, and bio-based material (i.e., biomass and bio-oil). Dimethyl ether can be produced from CO2 to prevent greenhouse gas emissions. This review aims to summarize recent progress in the field of innovative catalysts for the direct synthesis of dimethyl ether from syngas (CO+H2) and operating conditions. The problems of this process have been raised based on the yield and selectivity of dimethyl ether. However, regardless of how syngas is produced, the estimated total capital and operating costs in the industrial process depend on the type of reactor and the separation method.