Fossil-based heteroatom-containing compounds are crucial core scaffolds or key intermediates
in a wide range of pharmaceutical molecules, fiber dyes and printing ink (Li et al.,
2019a; Wu et al., 2020; Wu et al., 2021), which can also be directly used as solvents,
surfactants, and so on (Li et al., 2019b; Wu et al., 2019; Xu et al., 2019). However,
mainly owing to the dependence and overuse of fossil source, the environmental pollution/deterioration
and greenhouse effect are becoming increasingly prominent. In this regard, sustainability
is deemed as a key parameter for the future of producing heteroatom-containing compounds
and environmental enhancement, which not only requires the replacement of the fossil
fuel feedstocks by other renewable resources (e.g., non-food biomass), but also needs
the adoption of circular utilisation methods to prevent leakage of any ingredient
into the environment (Iglesias et al., 2020).
This Research Topic is Volume II of a series, and here we present a collection of
original research and review articles (20 papers in total) with topics on green and
sustainable chemistry, including catalytic conversion of biomass feedstocks (Liu et
al., Zhu et al., Liu et al., Zhang et al., Sun et al., Yao et al., Zhou et al., Zhao
et al., Yang et al., and Zhou et al.), biodiesel production (Wu et al., Zhang et al.,
and Liu et al.), and green synthesis of heteroatom-containing bioactive compounds
and functional materials (Wang et al., Pan et al., Chen et al., Pan et al., Zhang
et al., and Bao et al.). Also, the Research Topic provides interesting insights into
the green photocatalysis of organic pollutants (Zhang et al.).
Original research paper of Zhou et al. reports the controllable preparation of three
kinds of Fe-based composite catalysts with different Fe loadings for efficient hydrogen
production from biomass steam gasification. When the mass fraction of loading is 10%,
Fe species are well dispersed on the carrier, affording a high gas yield of 60.4%
(with 42.2% hydrogen proportion). Zhang et al. use glycerol waste to comparatively
evaluate the ameliorative effect on lignocellulose under microwave or conventional
heating method. During fast pyrolysis, levoglucosan produced from microwave-treated
samples (32.9%) was far more selective than the conventional heating group (18.8%),
and the content of aldehydes (high toxicity to the downstream fermentation) after
glycerol waste and microwave pretreatment was decreased by 2.5 times compared with
the untreated counterpart. In addition to directly using raw biomass resources, simple
sugars like fructose can be efficiently converted to 5-hydroxymethylfurfural (up to
82% yield) by dehydration over a stable Ti-doped SBA-15 catalyst in DMSO at 140°C
for 1 h (Zhu et al.), or to 5-ethoxymethylfurfural (80.4% yield) by cascade dehydration-etherification
using a UIO-66-SO3H catalyst in ethanol under the same thermal conditions (Zhao et
al.). Zhang et al. manufacture a biomass-based solid acid catalyst (SiO2@Cs-SO3H)
with a large specific surface area (21.82 m2/g) and acidity (3.47 mmol/g) using renewable
chitosan as raw material through sulfonation procedure under relatively mild conditions,
which is active for esterification of oleic acid and methanol to produce biodiesel
(98.2% yield).
The work of Chen et al. reports an unprecedented inactivation process of the indanol-derived
NHC catalysts bearing N-C6F5 groups, giving an unexpected multi-cyclic complex product
from the 3-component reaction with 1-methylcyclopropyl-carbaldehyde, 2,2,2-trifluoroacetophenone
and the NHC catalyst. Pan et al. develop an acid-catalyzed 2-alkylation of indole
molecules catalyzed by traceless HI, and 2,3-disubstituted indole molecules bearing
congested tertiary carbon centers are obtained in moderate to good yields. Some functional
catalytic materials such as hierarchical porous SAPO-34 (Wang et al.), bimetallic
Zn-Zr metal-organic framework (Zhang et al.), and graphene oxide-silver nanoparticles
composite (Bao et al.) are prepared in sustainable ways, and found to be efficient
for the synthesis of value-added chemicals (e.g., 4,6-dimethyldibenzothiophene) or
degradation of organic pollutants.
This Research Topic features several review articles with distinct scopes (Liu et
al., Sun et al., Zhou et al., Yang et al., Yao et al., Liu et al., Wu et al., Liu
et al., Pan et al., and Zhang et al.). Liu et al. review the application of recyclable
heterogeneous non-noble Zr/Hf-containing catalysts (e.g., Zr/Hf-containing metal oxides,
supported materials, zeolites, metal organic frameworks, metal organic hybrids) with
acid-base bifunctionality for catalytic transfer hydrogenation using the safe liquid
hydrogen donor, with emphasis on evaluating the reaction mechanisms and conversion
pathways. In a more detailed manner, the research progress of catalytic synthesis
of γ-valerolactone from furfural by Zr/Hf-based catalysts is reviewed by Sun et al.,
and the effects and regulation approaches of Lewis acid-base and Brønsted acid sites
in the catalysts on each steps in the reaction process are discussed. Zhou et al.
reveal the significance and potential of using titanate nanotubes-based materials
as sustainable and environmentally benign solid catalysts/supports for synthesis of
various bio-based chemicals, such as glycerol-derived solketal, jet fuel range alkanes
precursors, biomass-derived esters, aldehydes, and aromatic compounds. Yang et al.
propose the research development trend for improving the institutional mechanism of
the utilization of crop straw resources, strengthening technology research and development,
exploring the economic model of green cycle agriculture, accelerating the construction
of the industrial system, and designing new paths of resource utilization in multiple
ways. Yao et al. mainly review some latest studies about the conversion of cellulose
to 5-hydroxymethylfurfural catalyzed by solid acids with Brønsted and/or Lewis acidic
sites, such as sulfonated solid acids, carbon-based acids, and zeolites. Liu et al.
summarize the mechanisms of several important processes of producing 5-ethoxymethylfurfural
from lignocellulosic biomass-derived sugars and the research progress of the developed
acid catalysts. In addition, advancements in tobacco (Nicotiana tabacum L.) seed oils
(Wu et al.) and lipid extraction from microalgae using green solvents (Liu et al.)
for biodiesel production are also collected. For some structurally somplex natural
products such as sex pheromones (Pan et al.), and momilactones and related 9β-H pimarane
skeleton (Zhang et al.), the recent advances in their synthetic strategies with the
involved challenges are overviewed.
We wish this Research Topic attracts interested colleagues, enlightening more eco-friendly
and sustainable synthetic procedures, shedding light on renewed catalytic strategies
and routes developed for the production of bio-based heteroatom-containing compounds,
and providing enthusiasm in research and studies. Enjoy its reading!