Contents lists available at ScienceDirect Fuel Processing Technology journal homepage: www.elsevier.com/locate/fuproc Invited review article Recent developments in lignocellulosic biomass catalytic fast pyrolysis: Strategies for the optimization of bio-oil quality and yield Xu Chen, Qingfeng Che, Shujuan Li, Zihao Liu, Haiping Yang ⁎ , Yingquan Chen, Xianhua Wang, Jingai Shao, Hanping Chen State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, 1037 Luoyu Road, 430074 Wuhan, PR China ARTICLE INFO Keywords: Biomass Catalytic fast pyrolysis Bio-oil High-quality High-yield ABSTRACT Catalytic fast pyrolysis (CFP) is an attractive approach to convert biomass to high-quality bio-oil through the deoxygenation of pyrolysis vapors in the form of H 2 O, CO, and CO 2 . However, the deoxygenation process comes at the expense of bio-oil yield. This review begins with recent progress on lignocellulosic biomass pyrolysis chemistry and techniques, and then focuses on the latest improvements to the design of advanced catalysts and novel CFP processes. It was found that basic metal oxides (e.g., MgO and CaO) are promising alternative catalysts to zeolites (such as ZSM-5) with respect to the preferred decarboxylation reaction, which merits additional investigation on their structure-function relationships in the future. Additionally, catalytic co-pyrolysis of bio- mass with waste plastics or waste tires over zeolites is an attractive approach from the viewpoint of preferred dehydration reactions and the high-value utilization of solid wastes. However, the physicochemical properties of the catalysts should be further adjusted. Furthermore, in spite of many interesting results reported in the lit- erature, quantitatively analysis and uniform data presentation format is necessary for the further development of CFP techniques. 1. Introduction With the increasing concerns of the environmental pollution and the energy crisis caused by fossil fuels overuse, the development of clean and renewable energy alternatives is extremely urgent. Lignocellulosic biomass, the only one carbon-containing renewable energy resource, has been identified as an attractive feedstock for producing renewable fuels and chemicals due to the potential of zero CO 2 emission, abundant availability and low cost [1]. According to the International Energy Agency, bioenergy would account for 10% of the world's primary en- ergy supply by 2035 [2]. To cleanly and efficiently utilize the lignocellulosic biomass re- sources, the development of suitable conversion techniques is particu- larly important [3]. Fast pyrolysis is a promising approach as it can convert lignocellulosic biomass into liquid products in a short period, and the resulting pyrolysis liquid, called bio-oil, can reach yields of up to 65–75 wt% [4]. For a better understanding of biomass pyrolysis technology and guiding bio-oil production, extensive research efforts have been conducted over the past years with focus on biomass pyr- olysis mechanism [5–7], and meanwhile, novel pyrolysis techniques, such as grinding pyrolysis, microwave pyrolysis, solar pyrolysis, and stepwise pyrolysis, etc., have also been developed [8–11]. Hence, there is a need for a comprehensive study to summarize the state-of-the-art advances in the aspects of biomass pyrolysis mechanism and technique. In spite of these achievements on biomass pyrolysis chemistry and technique, the crude bio-oil from biomass fast pyrolysis still remains a high oxygen content, which contributes to instability, low heating va- lues, high viscosities and high acidity; and it is unsuitable for direct use in the existing petroleum-based infrastructure [12]. Therefore, the crude bio-oil must be further upgraded to reduce the undesirable components and increase the content of useful compounds. Hydro- deoxygenation (HDO) of bio-oil [13] or pyrolysis vapors [14,15] is an effective bio-oil upgrading process. However, the harsh reaction con- ditions (high pressure), the use of high-cost noble catalysts or bifunc- tional metal-acid catalysts (such as transition metal carbides, nitrides, and phosphide catalysts), and the considerable consumption of hy- drogen blocked the development and utilization of HDO for bio-oil upgrading [16]. Alternatively, catalytic upgrading of the pyrolysis va- pors under inert atmosphere and atmospheric pressure, or catalytic fast pyrolysis process (CFP), is the other one promising approach to bio-oil upgrading [17,18]. With directly upgrading of uncondensed vapors using suitable https://doi.org/10.1016/j.fuproc.2019.106180 Received 1 May 2019; Received in revised form 5 August 2019; Accepted 5 August 2019 ⁎ Corresponding author. E-mail address: yhping2002@163.com (H. Yang). Fuel Processing Technology 196 (2019) 106180 0378-3820/ © 2019 Elsevier B.V. All rights reserved. T