Syngas produced by biomass and waste gasification processes must be adequately clean of tar compounds before being utilized in value-added applications. Syngas cleaning by tar cracking at high temperatures is a promising technique that can utilize different kinds of catalysts. However, their use is limited by the deposition of coke layers, which induces a masking phenomenon on the active surface, and, consequently, the rapid deactivation of the catalyst. This study addresses how the temperature (750 and 800°C) and the steam concentration (0% and 7.5%) can affect the extent of water–gas and reforming reactions between steam and coke deposits. Two catalysts were used: a market-available activated carbon and an iron-based alumina catalyst. The tests showed better performance of the Fe/γ-Al₂O₃ catalyst. A mass increase of the bed was measured in tests with both the catalysts, which confirms the deposition of the coke layer produced by tar dehydrogenation and carbonization. Scanning electronic microscopy-energy-dispersive X-ray analysis (SEM-EDX) and Raman spectroscopy were utilized to investigate the nature of coke layers over the catalyst surface, with the aim of acquiring information about their reactivity towards the water gas reaction. SEM-EDX observations indicate that the thickness of these carbon layers is less than 2 μm. Raman spectra suggest a negligible effect of the reaction temperature in the tested range and, in particular, that the amorphous nature of coke layers deposited in the presence of steam is relatively more graphitic than that obtained without steam.

中文翻译：

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不同催化剂热合成气清洁中焦油的蒸汽重整：去除效率和焦炭层表征

生物质和废物气化过程产生的合成气在用于增值应用之前必须充分清除焦油化合物。通过在高温下焦油裂解来清洁合成气是一种很有前途的技术，可以利用不同种类的催化剂。然而，它们的使用受到焦炭层沉积的限制，焦炭层会在活性表面引起掩蔽现象，从而导致催化剂快速失活。本研究探讨了温度（750 和 800°C）和蒸汽浓度（0% 和 7.5%）如何影响水煤气的程度以及蒸汽和焦炭沉积物之间的重整反应。使用了两种催化剂：市售活性炭和铁基氧化铝催化剂。测试表明Fe/γ-Al ₂ O _{3的性能更好}催化剂。在两种催化剂的测试中测量了床的质量增加，这证实了焦油脱氢和碳化产生的焦炭层的沉积。利用扫描电子显微镜-能量色散 X 射线分析 (SEM-EDX) 和拉曼光谱研究了催化剂表面焦炭层的性质，目的是获取有关它们对水煤气反应的反应性的信息。SEM-EDX 观察表明这些碳层的厚度小于 2 μm。拉曼光谱表明在测试范围内反应温度的影响可以忽略不计，特别是在蒸汽存在下沉积的焦炭层的无定形性质比没有蒸汽时获得的焦炭层的石墨化程度相对更高。